CBSE 10TH Science
Science
Class X
(CODE NO:086/90)
- As per CCE guidelines the syllabus of Science for class X has been divided term wise.
- The units specified for each term shall be assessed through both Formative and Summative assessments.
- In each term, there will be two formative assessments each carrying 10% weightage.
- The summative assessment in the first term will carry 20% weightage and the summative assessment in the second term will carry 40% weightage.
- Hands on practical examination will be conducted through formative assessment once in every term with 20% weightage of total term marks.
- Assessment of Practical skills through MCQ will carry 20% weightage in every term end summative assessment.
COURSE STRUCTURE CLASS X
| FIRST TERM | MARKS-80 |
| UNITS | MARKS |
| I Chemical Substances
Chemical reaction; Acids, bases and salts, Metals and Non Metal |
29
S |
| II World of living
Life process; control and coordination in animals and plants |
19 |
| III Effects of current
Magnetic effects of currents |
26 |
| IV Natural Resources
Sources of Energy |
06 |
| TOTAL | 80 |
| SECOND TERM | MARKS-80 |
| UNITS | MARKS |
| I Chemical Substances
Carbon compounds; Periodic classification of elements |
21 |
| II World of living
Reroduction; Heridity and evolution |
27 |
| III Natural Phenomena | 26 |
| IV Natural Resources
Conservation of natural resources; the regional environment; our environment |
06 |
| TOTAL | 80 |
Science (Chemistry , Physics , Biology ) Syllabus 2010 - CBSE Class X
COURSE STRUCTURE
CLASS X (Theory)
One Paper Time : 21/2 hours Marks : 60
Unit Marks
I. Chemical Substances 18
II. World of living 16
III. Effects of Current 10
IV. Light 8
V. Natural Resources 8
Total 60
Theme : Materials (55 Periods)
Unit 1 : Chemical Substances - Nature and Behaviour
Acids, bases and salts : General properties, examples and uses, concept of pH scale, importance of pH in everyday life; preparation and uses of sodium hydroxide, Bleaching powder, Baking soda, washing soda and Plaster of Paris.
Chemical reactions : Chemical Equation, Types of chemical reactions : combination, decomposition, displacement, double displacement, precipitation, neutralization, oxidation and reduction in terms of gain and loss of oxygen and hydrogen.
Metals and non metals : General properties of Metals and Non-metals, reactivity series, Formation and properties of ionic compounds, Basic Metallurgical processes, corrosion and its prevention.
Carbon Compounds : Covalent bonding in carbon compounds. Versatile nature of carbon, Nomenclature of carbon compounds, Functional groups, difference between saturated hydrocarbons and unsaturated hydrocarbons, Ethanol and Ethanoic acid (only properties and uses), soaps and detergents.
Periodic classification of elements : Modern Periodic table, Gradation in Properties.
Theme : The world of the living (50 Periods)
Unit 2 : World of Living
Life Processes : "living" things; Basic concept of nutrition, respiration, transport and excretion in plants and animals.
Control and Co-ordination in animals and plants : Tropic movements in plants; Introduction to plant hormones; control and co-ordination in animals : voluntary, involuntary and reflex action, nervous system; chemical co-ordination : animal hormones.
Reproduction : Reproduction in animal and plants (asxual and sxual). Need for and methods of family planning. Safe sx vs HIV/AIDS. Child bearing and women's health.
Heridity and evolution : Heridity; Origin of life : brief introduction; Basic concepts of evolution.
Theme : How things work. (35 Periods)
Unit 3 : Effects of Current
Potential difference and electric current. Ohm's law; Resistance, Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors; Heating effect of Electric current; Electric Power, Inter relation between P, V, I and R.
Magnets : Magnetic field, field lines, field due to a current carrying wire, field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming's left hand rule. Electro magnetic induction. Induced potential difference, Induced current. Fleming's Right Hand Rule, Direct current. Alternating current; frequency of AC. Advantage of AC over DC. Domestic electric circuits.
Theme : Natural Phenomena (20 Periods)
Unit 4 : Reflection of light at curved surfaces, Images formed by spherical mirrors, centre of curvature, principalaxis, principal focus, focal length. Mirror Formula (Derivation not required), Magnification. Refraction; laws of refraction, refractive index.Refraction of light by spherical lens, Image formed by spherical lenses, Lens formula (Derivation not required),Magnification. Power of a lens; Functioning of a lens in human eye, problems of vision and remedies, applications of
spherical mirrors and lenses.Refraction of light through a prism, dispersion of light, scattering of light, applications in daily life.
Theme : Natural Resources (20 Periods)
Unit 5 : Conservation of natural resources : Management of natural resources. Conservation and judicious use of natural resources. Forest and wild life, coal and petroleum conservation. Examples of People's participationfor conservation of natural resources.
The Regional environment : Big dams : advantages and limitations; alternatives if any. Water harvesting. Sustainability of natural resources.
Sources of energy : Different forms of energy, conventional and non-conventional sources of energy: fossil fuels, solar energy; biogas; wind, water and tidal energy; nuclear. Renewable versus non-renewable sources.
Our Environment : Eco-system, Environmental problems, their solutions. Biodegradable and non-biodegradable, substances ozone depletion.
PRACTICALS
LIST OF EXPERIMENTS
Marks : 40 (20 + 20 )
1. To find the pH of the following samples by using pH paper/universal indicator.
i) Dilute Hydrochloric acid
ii) Dilute NaOH solution
iii) Dilute Ethanoic acid solution
iv) Lemon juice
v) Water
vi) Dilute Sodium Bicarbonate Solution.
2. To study the properties of acids and bases HCl & NaOH by their reaction with
i) Litmus solution (Blue/Red)
ii) Zinc metal
iii) Solid Sodium Carbonate
3. To determine the focal length of 72
a) Concave mirror
b) Convex lens by obtaining the image of a distant object.
4. To trace the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Measure the angle of incidence, angle of refraction, angle of emergence and interpret the result.
5. To study the dependence of current (I) on the potential difference (V) across a resistor and determine its resistance. Also plot a graph between V and I.
6. To determine the equivalent resistance of two resistors when connected in series.
7. To determine the equivalent resistance of two resistors when connected in parallel.
8. To prepare a temporary mount of a leaf peel to show stomata.
9. To show experimentally that light is necessary for photosynthesis.
10. To show experimentally that carbon dioxide is given out during respiration.
11. To study (a) binary fission in Amoeba and (b) budding in yeast with the help of prepared slides.
12. To determine the percentage of water absorbed by raisins.
13. To perform and observe the following reactions and classify them into:
i) Combination Reaction
ii) Decomposition Reaction
iii) Displacement Reaction
iv) Double Displacement Reaction
1. Action of water on quick lime.
2. Action of heat on Ferrous Sulphate crystals
3. Iron Nails kept in copper sulphate solution
4. Reaction between Sodium sulphate and Barium chloride solutions.
14. a) To observe the action of Zn, Fe, Cu and Al metals on the following salt solutions.
i) ZnSO4 (aq.)
ii) FeSO4 (aq.)
iii) CuSO4 (aq.)
iv) Al2 (SO4)3 (aq.)
b) Arrange Zn, Fe, Cu and Al metals in the decreasing order of reactivity based on the above result.
15. To study the following properties of acetic acid (ethanoic acid) :
73
i) odour
ii) solubility in wate
iii) effect on litmus
iv) reaction with sodium bicarbonate
SCHEME OF EVALUATION :
External Examination (to be conducted by the Board through multiple choice type written test) 20 Marks
School-based hands-on practical examination. 20 Marks
RECOMMENDED BOOKS :
Science - Textbook for class IX - NCERT Publication
Science - Textbook for class X - NCERT Publication
Assessment of Practical Skills in Science - Class IX - CBSE Publication
Assessment of Practical Skills in Science - Class X - CBSE Publication
CBSE Science Chap 1 - Chemical Reactions and Equations
Chapter Summary
- A complete chemical equation represents the reactants, products and their physical states symbolically.
- A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.
- In a combination reaction two or more substances combine to form a new single substance.
- Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.
- Reactions in which heat is given out along with the products are called exothermic reactions.
- Reactions in which energy is absorbed are known as endothermic reactions.
- When an element displaces another element from its compound, a displacement reaction occurs.
- Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
- Precipitation reactions produce insoluble salts.
- Reactions also involve the gain or loss of oxygen or hydrogen by substances.
- Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.
NCERT Book Solutions
NCERT Solutions - Chemical Reactions and Equations - Page 14 - Q1
1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
(i) (a) and (b)
Chap 1 - Chemical Reactions and Equations - Page 6 - Q2
2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
| 2 (i) | H2 + Cl2 -----------> 2HCl |
| 2 (ii) | 3BaCl2 + Al2(SO4)3 -------------> 3BaSO4 + 2AlCl3 |
| 2 (iii) | 2Na + 2H2O -----------------> 2NaOH + H2 |
Chap 1 - Chemical Reactions and Equations - Page 6 - Q3
3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
| 3 (i) | BaCl2 + Na2SO4 ---------------> BaSO4 + 2NaCl |
| 3 (iI) | NaOH + HCl -----------------> NaCl + H2O |
Chap 1 - Chemical Reactions and Equations - Page 6 - Q1
1. Why should a magnesium ribbon be cleaned before burning in air?
When Magnesium ribbon is stored, it reacts with oxygen to form a layer magnesium oxide . This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen.And Hence a magnesium ribbon should be cleaned before burning in air.
NCERT Solutions - Chemical Reactions and Equations - Page 10 - Q1
1. A solution of a substance ‘X’ is used for white washing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
| 1 (i) | The substance is calcium oxide ( Quick Lime) . Its Formula is CaO |
| 1 (ii) | CaO + H2O -----------> Ca(OH)2 |
NCERT Solutions - Chemical Reactions and Equations - Page 10 - Q2
2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
During electrolysis of water , hydrogen and oxygen gases are produced . Water (H2O) contains two parts hydrogen and one part oxygen.Since hydrogen goes to one test tube and oxygen goes to another, the amount of hydrogen gas in one of the test tubes is double of the amount of oxygen gas collected in the other tube.
NCERT Solutions - Chemical Reactions and Equations - Page 13 - Q1
1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
When an iron nail is placed in a copper sulphate solution, iron displaces copper from copper sulphate solution forming iron sulphate, which is green in colour. And hence the colour of copper sulphate solution change when an iron nail is dipped in it.
NCERT Solutions - Chemical Reactions and Equations - Page 13 - Q2
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride is a example of a double displacement reaction.
NCERT Solutions - Chemical Reactions and Equations - Page 13 - Q3
3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
| 3 (i) | Sodium is oxidised to Sodium Oxide and Oxygen is reduced. |
| 3 (ii) | CuO is reduced to Cu and Hydrogen is oxidised to H2O |
NCERT Solutions - Chemical Reactions and Equations - Page 14 - Q2
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
(d) displacement reaction.
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q10
Human Beings need energy to stay alive. We get this energy from the food we eat. During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration. Energy is released in the process and hence exothermic reaction.
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q11
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
In a decomposition reaction, a single substance decomposes to give two or more substances. Whereas In a combination reaction two or more substances combine to form a new single substance. And hence ,Decomposition reactions are opposite to combination reactions.
Decomposition Reaction : AB + Energy ----------> A + B
CaCO3(s) -----Heat----------- > CaO(s) + CO2(g)
Composition Reaction : A + B --------------> AB + Energy
Example : Burning of coal
C(s) + O2(g) → CO2(g)
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q3
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
(a) Hydrogen gas and iron chloride are produced.
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q4
4. What is a balanced chemical equation? Why should chemical equations be balanced?
A chemical equation is balanced when the numbers of atoms of each type involved in a chemical reaction are same on both the reactant and product sides of the equation.
As perthe law of conservation of mass that mass can neither be created nor destroyed in a chemical reaction. That is, the
total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. And Hence chemical equations must always be balanced.
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q5
5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
| 5 (a) | 3H2 + N2 --------------> 2NH3 |
| 5 (b) | 2H2S + 302 ----------------------> 2H2O + 2SO2 |
| 5 (c) | 3BaCl2 + Al2(SO4)3 ---------------------> 2AlCl3 + 3BaSO4 |
| 5 (d) | 2K + 2H2O --------> 2KOH + H2 |
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q6
6. Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q7
7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
| 7 (a) | Ca(OH)2 + CO2 ------------> CaCO3 + H2O |
| 7 (b) | Zn + 2AgNO3 -------------> Zn(NO3)2 + 2Ag |
| 7 (c) | 2Al + 3CuCl2 ----------> 2AlCl3 + 3Cu |
| 7 (d) | BaCl2 + K2SO4 ---------> BaSO4 + 2KCl |
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q8
8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
| 8 (a) | 2KBr + BaI2 --------> 2KI + BaBr2 , Double Displacement Reaction |
| 8 (b) | ZnCO3 -------> ZnO + CO2 , Decomposition Reaction |
| 8 (c) | H2 + Cl2 ------------------> 2HCl , Composition Reaction |
| 8 (d) | Mg + 2HCl ----------> MgCl2 + H2 , Displacement Reaction |
NCERT Solutions - Chemical Reactions and Equations - Page 15 - Q9
9. What does one mean by exothermic and endothermic reactions? Give examples.
Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.
Examples of exothermic reactions are –
Burning of natural gas
CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)
Reactions in which energy is absorbed are known as endothermic reactions.
Examples of endothermic reactions are –
2AgBr(s) -----------Sunlight -----> 2Ag(s) + Br2(g)
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q12
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
| Heat | CaCO3(s) -----------Heat→ CaO(s) + CO2(g) |
| Light | 2AgBr(s) -----------Sunlight→2Ag(s) + Br2(g) |
| Electricity | 2Al2O3 --------------> 4Al + 3O2 |
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q13
13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
When an element displaces another element from its compound, a displacement reaction occurs. Whereas two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
Displacement Reaction
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
Double Displacement Reaction
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q14
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
AgNO3 + Cu ----------> Cu(NO3)2 + 2Ag
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q15
15. What do you mean by a precipitation reaction? Explain by giving examples.
Any reaction that produces a precipitate can be called a precipitation reaction.Precipitation reactions produce insoluble salts.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
The white precipitate of BaSO4 is formed by the reaction of SO42– and Ba2+. The other product formed is sodium chloride
which remains in the solution.
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q16
16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
(a) Oxidation : Oxidation is the gain of oxygen or loss of hydrogen.
(b)Reduction : Reduction is the loss of oxygen or gain of hydrogen.
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q17
17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
The element ‘X’ is Copper and the black coloured compound is Copper Oxide (CuO) .The Chemical reaction is
2Cu + O2 ---------------Heat→2CuO
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q18
18. Why do we apply paint on iron articles?
Iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process
is commonly known as rusting of iron (Corrosion) . Corrosion causes damage to car bodies, bridges, iron railings, ships
and to all objects made of metals, specially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron. And hence to avoid rusting of iron , paint is applied on iron articles.
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q19
19. Oil and fat containing food items are flushed with nitrogen. Why?
When fats and oils are oxidised, they become rancid and their smell and taste change. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Nitrogen is an inert gas and act as an antioxidant to prevent rancidity of Oil and fat containing food items.
Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised
NCERT Solutions - Chemical Reactions and Equations - Page 16 - Q20
20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
(a) Corrosion: When a metal is attacked by substancesa round it such as moisture, acids, etc., it is said to corrode and this
process is called corrosion.
The black coating on silver and the green coating on copper are other examples of corrosion.
(b) Rancidity : When fats and oils are oxidised and their smell and taste change. This process is known as Rancidity
Examples : Butter when kept in open for long time , tastes and smell bad.
CBSE Science Chap 2 - Acids, Bases and Salts
Chapter Summary
- Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases.
- Acidic nature of a substance is due to the formation of H+(aq) ions in solution. Formation of OH–(aq) ions in solution is responsible for the basic nature of a substance.
- When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.
- When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen.
- When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water.
- Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
- The strength of an acid or an alkali can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution.
- A neutral solution has a pH of exactly 7, while an acisolution has a pH less than 7 and a basic solution a pH more than 7.
- Living beings carry out their metabolic activities within an optimal pH range.
- Mixing concentrated acids or bases with water is a highly exothermic process.
- Acids and bases neutralise each other to form corresponding salts and water.
- Water of crystallisation is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.
- Salts have various uses in everyday life and in industries.
NCERT Book Solutions
NCERT Solutions - Acids , Bases and Salts - Page 18 - Q1
1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Bases change the colour of the red litmus to blue.
NCERT Solutions - Acids , Bases and Salts - Page 22 - Q1
1. Why should curd and sour substances not be kept in brass and copper vessels?
NCERT Solutions - Acids , Bases and Salts - Page 22 - Q2
2. Which gas is usually liberated when an acid reacts with a metal?
Illustrate with an example. How will you test for the presence of this gas?
NCERT Solutions - Acids , Bases and Salts - Page 22 - Q3
3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds
formed is calcium chloride.
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q1
1. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q2
2. Why does an aqueous solution of an acid conduct electricity?
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q3
3. Why does dry HCl gas not change the colour of the dry litmus paper?
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q4
4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q5
5. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
NCERT Solutions - Acids , Bases and Salts - Page 25 - Q6
6. How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
NCERT Solutions - Acids , Bases and Salts - Page 33 - Q1
1. What is the common name of the compound CaOCl2?
NCERT Solutions - Acids , Bases and Salts - Page 33 - Q2
2. Name the substance which on treatment with chlorine yields bleaching powder.
NCERT Solutions - Acids , Bases and Salts - Page 33 - Q3
3. Name the sodium compound which is used for softening hard water.
NCERT Solutions - Acids , Bases and Salts - Page 33 - Q5
5. Write an equation to show the reaction between Plaster of Paris and water.
NCERT Solutions - Acids , Bases and Salts - Page 33- Q4
4. What will happen if a solution of sodium hydrocarbonate is heated?
Give the equation of the reaction involved.
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q1
1. A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q2
2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky.
The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q3
3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q5
5. Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q6
6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
NCERT Solutions - Acids , Bases and Salts - Page 34 - Q7
7. Why does distilled water not conduct electricity, whereas rain water does?
NCERT Solutions - Acids , Bases and Salts - Page 34- Q4
4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
NCERT Solutions - Acids , Bases and Salts - Page 35- Q8
8. Why do acids not show acidic behaviour in the absence of water?
NCERT Solutions - Acids , Bases and Salts - Page 35- Q9
9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
NCERT Solutions - Acids , Bases and Salts - Page 35 - Q10
10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
NCERT Solutions - Acids , Bases and Salts - Page 35 - Q11
11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
NCERT Solutions - Acids , Bases and Salts - Page 35 - Q12
12. A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
NCERT Solutions - Acids , Bases and Salts - Page 35 - Q13
13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
NCERT Solutions - Acids , Bases and Salts - Page 35 - Q14
14. What is a neutralisation reaction? Give two examples.
CBSE Science Chap 3 - Metals and Non-metals
Chapter Summary
- Elements can be classified as metals and non-metals.
- Metals are lustrous, malleable, ductile and are good conductors of heat and
- electricity. They are solids at room temperature, except mercury which is a liquid.
- Metals can form positive ions by losing electrons to non-metals.
- Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides.
- Different metals have different reactivities with water and dilute acids.
- A list of common metals arranged in order of their decreasing reactivity is known as an activity series.
- Metals above hydrogen in the Activity series can displace hydrogen from dilute acids. A more reactive metal displaces a less reactive metal from its salt solution.
- Metals occur in nature as free elements or in the form of their compounds.
- The extraction of metals from their ores and then refining them for use is known as metallurgy.
- An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
- The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.
- Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.
- Non-metals form negatively charged ions by gaining electrons when reacting with metals.
- Non-metals form oxides which are either acidic or neutral.
- Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.
NCERT Book Solutions
CBSE Science Chap 3 - Metals and Non-metals - P40 - Q1
Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
CBSE Science Chap 3 - Metals and Non-metals - P40 - Q2
Explain the meanings of malleable and ductile.
CBSE Science Chap 3 - Metals and Non-metals - P46 - Q1
Why is sodium kept immersed in kerosene oil?
CBSE Science Chap 3 - Metals and Non-metals - P46 - Q2
Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
CBSE Science Chap 3 - Metals and Non-metals - P46 - Q3
Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.
Metal Iron (II) sulphate Cooper (II) sulphate Zinc sulphate Silver nitrate
A. No reaction Displacement
B. Displacement No reaction
C. No reaction No reaction No reaction Displacement
D. No reaction No reaction No reaction No reaction
Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
CBSE Science Chap 3 - Metals and Non-metals - P46 - Q4
Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
CBSE Science Chap 3 - Metals and Non-metals - P46 - Q5
What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
CBSE Science Chap 3 - Metals and Non-metals - P49 - Q1
(i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
CBSE Science Chap 3 - Metals and Non-metals - P49 - Q2
Why do ionic compounds have high melting points?
CBSE Science Chap 3 - Metals and Non-metals - P53 - Q1
Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
CBSE Science Chap 3 - Metals and Non-metals - P53 - Q1
Defin the following terms.
(i) Mineral (ii) Ore (iii) Gangue
CBSE Science Chap 3 - Metals and Non-metals - P53 - Q2
Name two metals which are found in nature in the free state.
CBSE Science Chap 3 - Metals and Non-metals - P53 - Q3
What chemical process is used for obtaining a metal from its oxide?
CBSE Science Chap 3 - Metals and Non-metals - P55 - Q1
Metallic oxides of zinc, magnesium and copper were heated with the following metals.
|
Metal |
Zinc |
Magnesium |
Copper |
|
Zinc oxide |
- |
- |
- |
|
Magnesium oxide |
- |
- |
- |
|
Copper oxide |
- |
- |
- |
In which cases will you find displacement reactions taking place?
CBSE Science Chap 3 - Metals and Non-metals - P55 - Q2
Which metals do not corrode easily?
CBSE Science Chap 3 - Metals and Non-metals - P55 - Q3
What are alloys?
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q1
Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal.
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q2
Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) all of the above.
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q3
An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q4
Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q5
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q6
What are amphoteric oxides? Give two examples of amphoteric oxides.
CBSE Science Chap 3 - Metals and Non-metals - P56 - Q7
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q8
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q9
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(Fig)
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q10
State two ways to prevent the rusting of iron.
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q11
What type of oxides is formed when non-metals combine with oxygen?
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q12
Give reasons
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
CBSE Science Chap 3 - Metals and Non-metals - P57 - Q13
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
CBSE Science Chap 4 - Carbon and its Compounds
Chapter Summary
- Carbon is a versatile element that forms the basis for all living organisms and manyof the things we use.
- This large variety of compounds is formed by carbon because of its tetravalency and the property of catenation that it exhibits.
- Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell.
- Carbon forms covalent bonds with itself and other elements such as hydrogen ,oxygen, sulphur, nitrogen and chlorine.
- Carbon also forms compounds containing double and triple bonds between carbon atoms. These carbon chains may be in the form of straight chains, branched chains or rings.
- The ability of carbon to form chains gives rise to a homologous series of compounds which the same functional group is attached to carbon chains of different lengths.
- The functional groups such as alcohols, aldehydes, ketones and carboxylic acids bestow characteristic properties to the carbon compounds that contain them.
- Carbon and its compounds are some of our major sources of fuels.
- Ethanol and ethanoic acid are carbon compounds of importance in our daily lives.
- The action of soaps and detergents is based on the presence of both hydrophobic and hydrophilic groups in the molecule and this helps to emulsify the oily dirt and hence its removal.
NCERT Book Solutions
CBSE Science Chap 4 - Carbon and its Compounds - P61 - Q1
What would be the electron dot structure of carbon dioxide which has the formula CO2?
Electron dot structure of CO2 is
(IMAGES)
CBSE Science Chap 4 - Carbon and its Compounds - P61 - Q2
What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint − the eight atoms of sulphur are joined together in the form of a ring.)
Electron dot structure of a sulphur molecule
(IMAGES)
CBSE Science Chap 4 - Carbon and its Compounds - P68 - Q1
How many structural isomers can you draw for pentane?
CBSE Science Chap 4 - Carbon and its Compounds - P68 - Q2
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
The two features of carbon that give rise to a large number of compounds are as follows -
(i) Catenation − Carbon has the unique ability to form bonds with other atoms of carbon.
(ii) Tetravalency − With the valency of four, carbon is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.
CBSE Science Chap 4 - Carbon and its Compounds - P68 - Q3
What will be the formula and electron dot structure of cyclopentane?
CBSE Science Chap 4 - Carbon and its Compounds - P69 - Q4
Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal
*Are structural isomers possible for bromopentane?
CBSE Science Chap 4 - Carbon and its Compounds - P69 - Q5
How would you name the following compounds?
(i) (IMAGES)
(ii) (IMAGES)
(iiii)(IMAGES)
(i) Bromoethane
(ii) Methanal (formaldehyde)
(iii) Hexyne
CBSE Science Chap 4 - Carbon and its Compounds - P71 - Q1
Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
CBSE Science Chap 4 - Carbon and its Compounds - P71 - Q2
A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
(IMAGES)
When ethyne is burnt in air, it gives a sooty flame. The reason is incomplete combustion caused by limited supply of air. But when ethyne is burnt with oxygen, it gives a clean flame with temperature 3000°C due to complete combustion. This oxy-acetylene flame is used for welding and It is not possible to attain such a high temperature without mixing only oxygen. And for this reason, a mixture of ethyne and air is not used for welding.
CBSE Science Chap 4 - Carbon and its Compounds - P74 - Q1
How would you distinguish experimentally between an alcohol and a carboxylic acid?
Acid reacts with carbonate and hydrogen carbonate to evolve CO2 gas that turns lime water milky. Whereas alcohols do not react with carbonates and hydrogen carbonates. So we can distinguish between an alcohol and a carboxylic acid based on their reaction with carbonates and hydrogen carbonates.
CBSE Science Chap 4 - Carbon and its Compounds - P74 - Q2
What are oxidising agents?
Some substancesare capable of adding oxygen to others. These are known as oxidising agents.The examples of oxidising agents are alkaline potassium permanganate and acidified potassium dichromate
CBSE Science Chap 4 - Carbon and its Compounds - P76 - Q1
Would you be able to check if water is hard by using a detergent?
Detergents are ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water as well. Detergents do not react with calcium and magnesium ions present in hard water to form scum like soap does. They give a good amount of lather irrespective of whether the water is hard or soft. This means that detergents can be used in both soft and hard water. Hence, it cannot be used to check whether the water is hard or not.
CBSE Science Chap 4 - Carbon and its Compounds - P76 - Q2
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
A soap molecule has two parts known as hydrophobic and hydrophilic. With the help of these, it attaches to the grease or dirt particle and forms a cluster called micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion.To remove these micelles (entrapping the dirt), it is necessary to agitate clothes.
CBSE Science Chap 4 - Carbon and its Compounds - P77 - Q1
Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
(b) Ethane has 7 covalent bonds.
CBSE Science Chap 4 - Carbon and its Compounds - P77 - Q2
Butanone is a four-carbon compound with the functional group
(a) carboxylic acid.
(b) aldehyde.
(c) ketone.
(d) alcohol.
(c) The functional group of butanone is ketone.
CBSE Science Chap 4 - Carbon and its Compounds - P77 - Q3
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) the food is not cooked completely.
(b) the fuel is not burning completely.
(c) the fuel is wet.
(d) the fuel is burning completely.
(b) the fuel is not burning completely
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q4
Explain the nature of the covalent bond using the bond formation in CH3Cl.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q5
Draw the electron dot structures for
(a) ethanoic acid.
(b) H2S.
(c) propanone.
(d) F2.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q6
What is a homologous series? Explain with an example.
A homologous series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group.
For example, methane, ethane, propane, butane, etc. are all part of the alkane homologous series. The general formula of this series is CnH2n+2.
Methane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3¬CH2CH2CH3
It can be noticed that there is a difference of −CH2 unit between each successive compound.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q7
How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
• Ethanol is a liquid at room temperature with a pleasant odour while ethanoic acid has vinegar-like smell. The melting point of ethanoic acid is 17°C. This is below room temperature and hence, it freezes during winters.
• Ethanoic acid reacts with metal carbonates and metal hydrogencarbonates to form salt, water, and carbon dioxide gas while ethanol does not react with them.
(IMAGES)
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q8
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
A soap is a sodium or potassium salt of long chain fatty acids. It has one polar end and one non-polar end. The polar end is hydrophilic in nature i.e., this end is attracted towards water. The non-polar end is hydrophobic but lipophilic, i.e., it is attracted towards hydrocarbons. When soap is added to water, soap molecules arrange themselves in a cluster to keep the non-polar portion out of water such that the non-polar ends are in the interior of the cluster and the polar ends are on the surface of the cluster. Since the dirt present on clothes is organic in nature and insoluble in water, the hydrophobic ends of the clusters attach themselves to the dirt. This cluster formation in which the dirt is entrapped is the micelle.
(IMAGES)
Micelle formation does not occur in alcohol because the alkyl chain of soap becomes soluble in alcohol.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q9
Why are carbon and its compounds used as fuels for most applications?
Most of the carbon compounds give a lot of heat and light when burnt in air. Saturated hydrocarbons burn with a clean flame and no smoke is produced. The carbon compounds, used as a fuel, have high calorific values. Therefore, carbon and its compounds are used as fuels for most applications.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q10
Explain the formation of scum when hard water is treated with soap.
Soap does not work properly when the water is hard. A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q11
What change will you observe if you test soap with litmus paper (red and blue)?
Since soap is basic in nature, it will turn red litmus blue. However, the colour of blue litmus will remain blue.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q12
What is hydrogenation? What is its industrial application?
Hydrogenation is the process of addition of hydrogen. Unsaturated hydrocarbons are added with hydrogen in the presence of palladium and nickel catalysts to give saturated hydrocarbons.
(IMAGES)
This reaction is applied in the hydrogenation of vegetables oils, which contain long chains of unsaturated carbons.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q13
Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
Unsaturated hydrocarbons undergo addition reactions. Being unsaturated hydrocarbons, C3H6 and C2H2 undergo addition reactions.
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q14
Give a test that can be used to differentiate chemically between butter and cooking oil.
Butter contains saturated fats. Therefore, it cannot be hydrogenated. On the other hand, oil has unsaturated fats. That is why it can be hydrogenated to saturated fats (solids).
CBSE Science Chap 4 - Carbon and its Compounds - P78 - Q15
Explain the mechanism of the cleaning action of soaps.
Cleansing action of soaps:
The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water.
(IMAGES)
Chap 5 - Periodic Classification of Elements
Chap 5 - Periodic Classification of Elements - P81 - Q1
Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
Only one triad of Dobereiner’s triads exists in the columns of Newlands’ octaves. The triad formed by the elements Li, Na, and K of Dobereiner’s triads also occurred in the columns of Newlands’ octaves.
Dobereiner’s triads
|
Li |
Ca |
Cl |
|
Na |
Sr |
Br |
|
K |
Ba |
I |
Newlands’ octaves
|
H |
Li |
Be |
B |
C |
N |
O |
|
F |
Na |
Mg |
Al |
Si |
P |
S |
|
Cl |
K |
Ca |
Cr |
Ti |
Mn |
Fe |
|
Co and Ni |
Cu |
Zn |
Y |
In |
As |
Se |
|
Br |
Rb |
Sr |
Ce and La |
Zr |
− |
− |
Chap 5 - Periodic Classification of Elements - P81 - Q2
What were the limitations of Dobereiner’s classification?
Limitation of Dobereiner’s classification:
All known elements could not be classified into groups of triads on the basis of their properties.
Chap 5 - Periodic Classification of Elements - P81 - Q3
What were the limitations of Newlands’ Law of Octaves?
Limitations of Newlands’ law of octaves:
(i) It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
(ii) Those elements that were discovered after Newlands’ octaves did not follow the law of octaves.
(iii) The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
(iv) Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.
Chap 5 - Periodic Classification of Elements - P85 - Q1
Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.
K is in group 1. Therefore, the oxide will be K2O.
C is in group 4. Therefore, the oxide will be CO2.
Al is in group 3. Therefore, the oxide will be Al2O3.
Si is in group 4. Therefore, the oxide will be SiO2.
Ba is in group 2. Therefore, the oxide will be BaO.
Chap 5 - Periodic Classification of Elements - P85 - Q2
Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Scandium and germanium
Chap 5 - Periodic Classification of Elements - P85 - Q3
What were the criteria used by Mendeleev in creating his Periodic Table?
Mendeleev’s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals.
Chap 5 - Periodic Classification of Elements - P85 - Q4
Why do you think the noble gases are placed in a separate group?
Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.
Chap 5 - Periodic Classification of Elements - P90 - Q1
How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?
Mendeleev was unable to give fixed position to hydrogen and isotopes in the periodic table. In Mendeleev’s periodic table, the increasing manner of atomic mass of the elements is not always regular from one to its next. It was believed that a more fundamental property than atomic mass could explain periodic properties in a better manner.
It was Henry Moseley who demonstrated that atomic number of an element could explain periodic properties in a better way than atomic mass of an element and arranged the elements in increasing order of their atomic numbers. Then it was found that the various anomalies of Mendeleev’s periodic table were removed by the modern periodic table.
Chap 5 - Periodic Classification of Elements - P90 - Q2
Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is same in all these three elements. And since chemical properties are due to valence electrons, they show same chemical reactions.
Chap 5 - Periodic Classification of Elements - P90 - Q3
Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.
(a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.
Chap 5 - Periodic Classification of Elements - P90 - Q4
(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
(a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.
(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.
Chap 5 - Periodic Classification of Elements - P90 - Q5
In the Modern Periodic Table, which are the metals among the first ten elements?
Among the first ten elements, lithium (Li) and beryllium (Be) are metals.
Chap 5 - Periodic Classification of Elements - P90 - Q6
By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?
Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.
Chap 5 - Periodic Classification of Elements - P91 - Q1
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
(c) The atoms lose their electrons more easily.
(On moving from left to right across the periods of the periodic table, the non-metallic character increases. Hence, the tendency to lose electrons decreases.)
Chap 5 - Periodic Classification of Elements - P91 - Q2
Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na (b) Mg (c) Al (d) Si
(b) X would most likely be in the same group of the Periodic Table as magnesium (Mg).
Chap 5 - Periodic Classification of Elements - P91 - Q3
Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?
(a) Neon has two shells, both of which are completely filled with electrons (2 electrons in K shell and 8 electrons in L shell).
(b) Magnesium has the electronic configuration 2, 8, 2.
(c) Silicon has a total of three shells, with four electrons in its valence shell (2 electrons in K shell, 8 electrons in L shell and 4 electrons in M shell).
(d) Boron has a total of two shells, with three electrons in its valence shell (2 electrons in K shell and 3 electrons in L shell).
(e) Carbon has twice as many electrons in its second shell as in its first shell (2 electrons in K shell and 4 electrons in L shell).
Chap 5 - Periodic Classification of Elements - P91 - Q4
(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
(a) All the elements in the same column as boron have the same number of valence electrons (3). Hence, they all have valency equal to 3.
(b) All the elements in the same column as fluorine have the same number of valence electrons (7). Hence, they all have valency equal to 1.
Chap 5 - Periodic Classification of Elements - P91 - Q5
An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)
N(7) F(9) P(15) Ar(18)
(a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration as 2, 7.
Chap 5 - Periodic Classification of Elements - P92 - Q6
The position of three elements A, B and C in the Periodic Table are shown below −
|
Group 16 |
Group 17 |
|
− |
− |
|
− |
A |
|
− |
− |
|
B |
C |
(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
(a) A is a non-metal.
(b) C is less reactive than A, as reactivity decreases down the group in halogens.
(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
(d) A will form an anion as it accepts an electron to complete its octet.
Chap 5 - Periodic Classification of Elements - P92 - Q7
Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
|
Element |
K L M |
|
Nitrogen Phosphorus |
2 5 2 8 5 |
Nitrogen is more electronegative than phosphorus. On moving down a group, the number of shell increases. Therefore, the valence electrons move away from the nucleus and the effective nuclear charge decreases. This causes the decrease in the tendency to attract electron and hence electronegativity decreases.
Chap 5 - Periodic Classification of Elements - P92 - Q8
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
In the modern periodic table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same.
Elements across a period show an increase in the number of valence electrons.
Chap 5 - Periodic Classification of Elements - P92 - Q9
In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?
The element with atomic number 12 has same chemical properties as that of calcium. This is because both of them have same number of valence electrons (2).
Chap 5 - Periodic Classification of Elements - P92 - Q10
Compare and contrast the arrangement of elements in Mendeleev’s periodic Table and the Modern Periodic Table.
|
|
Mendeleev’s periodic table |
|
Modern periodic table |
|
1. |
Elements are arranged in the increasing order of their atomic masses. |
1. |
Elements are arranged in the increasing order of their atomic numbers. |
|
2. |
There are a total of 7 groups (columns) and 6 periods (rows). |
2. |
There are a total of 18 groups (columns) and 7 periods (rows). |
|
3. |
Elements having similar properties were placed directly under one another. |
3. |
Elements having the same valence shell are present in the same period while elements having the same number of valence electrons are present in the same group. |
|
4. |
The position of hydrogen could not be explained. |
4. |
Hydrogen is placed above alkali metals. |
|
5. |
No distinguishing positions for metals and non-metals. |
5. |
Metals are present at the left hand side of the periodic table whereas non-metals are present at the right hand side. |
Chap 6 - Life Processes
Chap 6 - Life Processes - P95 - Q1
1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells of multicellular organisms like humans.
Chap 6 - Life Processes - P95 - Q2
2. What criteria do we use to decide whether something is alive?
We tend to think of some sort of movement, either growth-related or not, as common evidence for being alive.But a plant that is not visibly growing is still alive, and some animals can breathe without visible movement. Thus Movements over very small scales will be invisible to the naked eye – movements of molecules, for example. Presense of this molecular level movements determines whether the organism is alive or not.
Chap 6 - Life Processes - P95 - Q3
3. What are outside raw materials used for by an organism?
Food and Oxygen are outside raw materials used for by an organism.
Chap 6 - Life Processes - P95 - Q4
4. What processes would you consider essential for maintaining life?
Life processes like respiration,nutrition, transportation, excretion are considered as essential for maintaining life.
Chap 6 - Life Processes - P101 - Q1
1. What are the differences between autotrophic nutrition and heterotrophic nutrition?
|
|
Autotrophic nutrition |
|
Heterotrophic nutrition |
|
(i) |
Food is synthesised from simple inorganic raw materials such as CO2 and water. |
(i) |
Food is obtained directly or indirectly from autotrophs. This food is broken down with the help of enzymes. |
|
(ii) |
Presence of green pigment (chlorophyll) is necessary. |
(ii) |
No pigment is required in this type of nutrition. |
|
(iii) |
Food is generally prepared during day time. |
(iii) |
Food can be prepared at all times. |
|
(iv) |
All green plants and some bacteria have this type of nutrition. |
(iv) |
All animals and fungi have this type of nutrition. |
Chap 6 - Life Processes - P101 - Q2
Where do plants get each of the raw materials required for photosynthesis?
Chap 6 - Life Processes - P101 - Q3
What is the role of the acid in our stomach?
Chap 6 - Life Processes - P101 - Q4
What is the function of digestive enzymes?
Chap 6 - Life Processes - P101 - Q5
How is the small intestine designed to absorb digested food?
Chap 6 - Life Processes - P105 - Q1
What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
Chap 6 - Life Processes - P105 - Q2
What are the different ways in which glucose is oxidized to provide energy in various organisms?
Chap 6 - Life Processes - P105 - Q3
How is oxygen and carbon dioxide transported in human beings?
Chap 6 - Life Processes - P105 - Q4
How are the lungs designed in human beings to maximize the area for exchange of gases?
Chap 6 - Life Processes - P110 - Q1
What are the components of the transport system in human beings? What are the functions of these components?
Chap 6 - Life Processes - P110 - Q2
Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Chap 6 - Life Processes - P110 - Q3
What are the components of the transport system in highly organised plants?
Chap 6 - Life Processes - P110 - Q4
How are water and minerals transported in plants?
Chap 6 - Life Processes - P110 - Q5
How is food transported in plants?
Chap 6 - Life Processes - P112 - Q1
Describe the structure and functioning of nephrons.
Chap 6 - Life Processes - P112 - Q2
What are the methods used by plants to get rid of excretory products?
Chap 6 - Life Processes - P112 - Q3
How is the amount of urine produced regulated?
Chap 6 - Life Processes - P113 - Q1
The kidneys in human beings are a part of the system for
(a) nutrition.
(b) respiration.
(c) excretion.
(d) transportation.
Chap 6 - Life Processes - P113 - Q2
The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
Chap 6 - Life Processes - P113 - Q3
The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.
Chap 6 - Life Processes - P113 - Q4
The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.
Chap 6 - Life Processes - P113 - Q5
How are fats digested in our bodies? Where does this process take place?
Chap 6 - Life Processes - P113 - Q6
What is the role of saliva in the digestion of food?
Chap 6 - Life Processes - P113 - Q7
What are the necessary conditions for autotrophic nutrition and what are its by-products?
Chap 6 - Life Processes - P113 - Q8
What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.
Chap 6 - Life Processes - P113 - Q9
How are the alveoli designed to maximise the exchange of gases?
Chap 6 - Life Processes - P113 - Q10
What would be the consequences of a deficiency of haemoglobin in our bodies?
Chap 6 - Life Processes - P113 - Q11
Describe double circulation in human beings. Why is it necessary?
Chap 6 - Life Processes - P113 - Q12
What are the differences between the transport of materials in xylem and phloem?
Chap 7 - Control and Coordination
Chap 7 - Control and Coordination - P119 - Q1
What is the difference between a reflex action and walking?
A reflex action is a Sudden action in response to something in the environment. In Other hand,Walking, is a voluntary action. It is under our conscious control
Chap 7 - Control and Coordination - P119 - Q2
What happens at the synapse between two neurons?
A chemical reaction that creates an electrical impulse. This impulse travels from the endrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the
gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron.
Chap 7 - Control and Coordination - P119 - Q3
Which part of the brain maintains posture and equilibrium of the body?
Cerebellum, is the part of the brain maintains posture and equilibrium of the body.
Chap 7 - Control and Coordination - P119 - Q4
How do we detect the smell of an agarbatti (incense stick)?
There are separate areas of association where this sensory information is
interpreted by putting it together with information from other receptors
as well as with information that is already stored in the brain. Based on
all this, a decision is made about how to respond and the information is
passed on to the motor areas which control the movement of voluntary
muscles,
Chap 7 - Control and Coordination - P119 - Q5
What is the role of the brain in reflex action?
commonly when we talk about some sudden action in response to something in the environment. this is the case, it is no surprise that the thinking tissue in our body consists of dense networks of intricately arranged neurons. It sits in the forward end of the skull, and receives signals from all over the body which it thinks about before responding to them. Obviously, in order to receive these signals, this thinking part of the brain in the skull must be connected to nerves coming from various parts of the body. Similarly, if this part of the brain is to instruct muscles to move, nerves must carry this signal back to different parts of the body.
Chap 7 - Control and Coordination - P122 - Q1
What are plant hormones?
coordinate growth, development and responses to the environment. They are synthesised at places away from where they act and simply diffuse to the area of action.
Chap 7 - Control and Coordination - P122 - Q2
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
The movement of leaves of the sensitive plant, “touch me not”, touch or contact stimuli. Plants show tropism in response to other stimuli as well. The roots of a plant occurs in response to always grow downwards while the shoots usually grow
upwards and away from the earth.
Chap 7 - Control and Coordination - P122 - Q3
Give an example of a plant hormone that promotes growth.
Auxin is an example of growth-promoting plant hormone.
Chap 7 - Control and Coordination - P122 - Q4
How do auxins promote the growth of a tendril around a support?
It help in the growth of the stem. Cytokinins promote cell division, and it is natural then that they are present in greater concentration in
areas of rapid cell division, such as in fruits and seeds
Chap 7 - Control and Coordination - P122 - Q5
Design an experiment to demonstrate hydrotropism.
Take two small beakers and label them as A and B. Fill beaker A with water. Now make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beaker A and beaker B, as shown in the figure. Attach few germinating seeds in the middle of the filter paper bridge. Now, cover the entire set-up with a transparent plastic container so that the moisture is retained.
(IMAGES)
Observation:
The roots of the germinating seeds will grow towards beaker A.
(IMAGES)
This experiment demonstrates the phenomenon of hydrotropism.
Chap 7 - Control and Coordination - P125 - Q1
How does chemical coordination take place in animals?
A chemical signal were to be sent as well, it would reach all cells of the body and provide the wideranging changes needed. This is done in many animals, including human beings, using a hormone called adrenaline that is secreted from the adrenal glands.
Chap 7 - Control and Coordination - P125 - Q1
Which of the following is a plant hormone?
(a) Insulin
(b) Thyroxin
(c) Oestrogen
(d) Cytokinin
(d) Cytokinin
Chap 7 - Control and Coordination - P125 - Q2
Why is the use of iodised salt advisable?
Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth.
Chap 7 - Control and Coordination - P125 - Q2
The gap between two neurons is called a
(a) dendrite.
(b) synapse.
(c) axon.
(d) impulse.
(b) synapse.
Chap 7 - Control and Coordination - P125 - Q3
How does our body respond when adrenaline is secreted into the blood?
Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it
acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles
Chap 7 - Control and Coordination - P126 - Q3
The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
(d) The brain is responsible for thinking, regulating the heart beat and balancing the body.
Chap 7 - Control and Coordination - P126 - Q4
Why are some patients of diabetes treated by giving injections of insulin?
The function of receptors are usually located in our sense organs, such as the
inner ear, the nose, the tongue, and so on.
It sits in the forward end of the skull, and receives signals from all over the
body which it thinks about before responding to them. Obviously, in
order to receive these signals, this thinking part of the brain in the skull
must be connected to nerves coming from various parts of the body.
Chap 7 - Control and Coordination - P126 - Q5
Draw the structure of a neuron and explain its function.
Neurons are the functional units of the nervous system. The three main parts of a neuron are axon, dendrite, and cell body.
(IMAGES)
Functions of the three parts of a neuron:
Axon: It conducts messages away from the cell body.
Dendrite: It receives information from axon of another cell and conducts the messages towards the cell body.
Cell body: It contains nucleus, mitochondria, and other organelles. It is mainly concerned with the maintenance and growth.
Chap 7 - Control and Coordination - P126 - Q6
How does phototropism occur in plants?
Environmental triggers such as light, or gravity will change the directions that plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it.
Chap 7 - Control and Coordination - P126 - Q7
Which signals will get disrupted in case of a spinal cord injury?
In case of any injury to the spinal cord, the signals coming from the nerves as well as the signals coming to the receptors will be disrupted.
Chap 7 - Control and Coordination - P126 - Q8
How does chemical coordination occur in plants?
cells around have the means to detect this compound using special molecules on their surfaces, then they would be able to recognise information, and even transmit it. This will be slower, of course, but it can potentially reach all cells of the body, regardless of nervous connections, and it can be done steadily and persistently. These compounds, or hormones used by multicellular organisms for control and coordination show a great deal of diversity,
Chap 7 - Control and Coordination - P126 - Q9
What is the need for a system of control and coordination in an organism?
This information, acquired at the end of the dendritic tip of a nerve cell sets off a chemical reaction that creates an electrical impulse. This impulse travels from the dendrite to the cell body, and then along the axon to its end. At the end of the axon, the electrical impulse sets off the release of some chemicals. These chemicals cross the
gap, or synapse, and start a similar electrical impulse in a dendrite of the next
neuron. This is a general scheme of how nervous impulses travel in the body. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland
Chap 7 - Control and Coordination - P126 - Q10
How are involuntary actions and reflex actions different from each other?
Involuntary actions cannot be consciously controlled. On the other hand, the reflex actions such as closing of eyes immediately when bright light is focused show sudden response and do not involve any thinking. This means that unlike involuntary actions, the reflex actions are not under the control of brain.
Chap 7 - Control and Coordination - P126 - Q11
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
|
|
Nervous system mechanism |
|
Hormonal system mechanism |
|
1. |
The information is contained in the form of electric impulse. |
1. |
The information is contained in the form of chemical messengers. |
|
2. |
The axons and dendrites trasfer the information through a coordinated effort. |
2. |
The information is transferred or transported through blood. |
|
3. |
The flow of information is huge and the response is quick. |
3. |
The information travels slowly and the response is slow. |
|
4. |
Its effects are short lived. |
4. |
It has prolonged effects. |
Chap 7 - Control and Coordination - P126 - Q12
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
|
|
Movement in sensitive plants |
|
Movement in our legs |
|
1. |
The movement that takes place in a sensitive plant such as Mimosa pudica occurs in response to touch (stimulus). |
1. |
Movement in our legs is an example of voluntary actions. |
|
2. |
For this movement, the information is transmitted from cell to cell by electro-chemical signals as plants do not have any specialised tissue for conduction of impulses. |
2. |
The signal or messages for these actions are passed to the brain and hence are consciously controlled. |
|
3. |
For this movement to occur, the plant cells change shape by changing the amount of water in them. |
3. |
In animal muscle cells, some proteins are found which allow the movement to occur. |
Chap 8 - How do Organisms Reproduce?
Chap 8 - How do Organisms Reproduce? - P128 - Q1
What is the importance of DNA copying in reproduction?
DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Reproduction is therefore linked to the stability of populations of species. However, niches can change because of reasons beyond the control of the organisms. Temperatures on earth can go up or down, water levels can vary, or there could be meteorite hits, to think of a few examples. If
a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive.
Chap 8 - How do Organisms Reproduce? - P128 - Q2
Why is variation beneficial to the species but not necessarily for the individual?
Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult.
Chap 8 - How do Organisms Reproduce? - P133 - Q1
How does binary fission differ from multiple fission?
In binary fission, a single cell divides into two equal halves. Amoeba and
Bacteria divide by binary fission
In multiple fission, a single cell divides into many daughter cells simultaneously. Amoeba and Plasmodium divide by multiple fission
Chap 8 - How do Organisms Reproduce? - P133 - Q2
How will an organism be benefited if it reproduces through spores?
• Large numbers of spores are produced in one sporangium.
• Spores are distributed easily by air to far-off places to avoid competition at one place.
• Spores are covered by thick walls to prevent dehydration under unfavourable conditions
Chap 8 - How do Organisms Reproduce? - P133 - Q3
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
The process of regeneration involves the formation of new organisms from its body parts. Simple organisms can utilize this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth and development. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration
Chap 8 - How do Organisms Reproduce? - P133 - Q4
Why is vegetative propagation practised for growing some types of plants?
The ability of the plants to reproduce by producing new plants from the vegetative plant parts such as leaf, stem, or roots under appropriate conditions However, this method of reproduction is also used for agricultural purposes in commercial production of some plants such as sugarcane, grapes, roses, etc.
Chap 8 - How do Organisms Reproduce? - P133 - Q5
Why is DNA copying an essential part of the process of reproduction?
DNA (Deoxyribonucleic acid) copying is an essential part of reproduction as it passes genetic information from parents to offspring. It determines the body design of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by division of a cell to form two cells.
Chap 8 - How do Organisms Reproduce? - P140 - Q1
How is the process of pollination different from fertilization?
transfer of pollens from anther to stigma. It occurs with the help of certain pollinators such as air, water, birds, or some insects.
Fertilization, on the other hand, is the fusion of the male and female gametes.
Chap 8 - How do Organisms Reproduce? - P140 - Q2
What is the role of the seminal vesicles and the prostate gland?
seminal vesicles and prostate glands lubricate the sperms and provide a fluid medium for easy transport of sperms
Chap 8 - How do Organisms Reproduce? - P140 - Q3
What are the changes seen in girls at the time of puberty?
Secondary sexual characteristics in girls:
• Increase in the size of uterus and ovary.
• Beginning of menstrual cycle.
• More secretion of oil from the skin, which results in the appearance of pimples.
Chap 8 - How do Organisms Reproduce? - P140 - Q4
How does the embryo get nourishment inside the mother’s body?
The embryo develops inside the mother’s body for about nine months. Inside the uterus, the outer tissue surrounding the embryo develops finger-like projections called villi. These villi are surrounded by uterine tissue and maternal blood.
Chap 8 - How do Organisms Reproduce? - P140 - Q5
If a woman is using a copper−T, will it help in protecting her from sexually transmitted diseases?
No. Using a copper-T will not provide a protection from sexually transmitted diseases, as it does not prevent the entry of semen.
Chap 8 - How do Organisms Reproduce? - P141 - Q1
Asexual reproduction takes place through budding in
(a) amoeba.
(b) yeast.
(c) plasmodium.
(d) leishmania
(b) Asexual reproduction takes place through budding in yeast
Chap 8 - How do Organisms Reproduce? - P141 - Q2
Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
(c) Vas deferens is not a part of the female reproductive system in human beings.
Chap 8 - How do Organisms Reproduce? - P141 - Q3
The anther contains
(a) sepals.
(b) ovules.
(c) carpel.
(d) pollen grains.
(d) The anther contains pollen grains
Chap 8 - How do Organisms Reproduce? - P141 - Q4
What are the advantages of sexual reproduction over asexual reproduction?
Advantages of sexual reproduction:
• In sexual reproduction, more variations are produced. Thus, it ensures survival of species in a population.
• The new formed individual has characteristics of both the parents.
• Variations are more viable in sexual mode than in asexual one. This is because in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
Chap 8 - How do Organisms Reproduce? - P141 - Q5
What are the functions performed by the testis in human beings?
• Produce sperms
• Produce a hormone called testosterone, which brings about secondary sexual characters in boys
Chap 8 - How do Organisms Reproduce? - P141 - Q6
Why does menstruation occur?
process occurs every month because one egg is released from the ovary every month and at the same time, the uterus (womb) prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo.
Chap 8 - How do Organisms Reproduce? - P141 - Q7
Draw a labelled diagram of the longitudinal section of a flower.
Chap 8 - How do Organisms Reproduce? - P141 - Q8
What are the different methods of contraception?
Natural method:
It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because during this period,
Barrier method : Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.
Oral contraceptives: These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur
Implants and surgical methods: It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Chap 8 - How do Organisms Reproduce? - P141 - Q9
How are the modes for reproduction different in unicellular and multicellular organisms?
In unicellular organisms, The modes of reproduction in unicellular organisms can be fission, budding, etc. whereas in multicellular organisms, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc.
Chap 8 - How do Organisms Reproduce? - P141 - Q10
How does reproduction help in providing stability to populations of species?
It helps in providing stability to the population of species by producing a new individual that resembles the parents. This is the reason why cats give birth to only cats or dogs give birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats or any other species
Chap 8 - How do Organisms Reproduce? - P141 - Q11
What could be the reasons for adopting contraceptive methods?
(i) To prevent unwanted pregnancies.
(ii) To control population rise or birth rate.
(iii) To prevent the transfer of sexually transmitted diseases
Chap 9 - Heredity and Evolution
Chap 9 - Heredity and Evolution - P143 - Q1
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
In asexual reproduction, the reproducing cells manufacture a copy of their DNA through some chemical reactions. However, this copying of DNA is not perfect.
if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A.
Chap 9 - Heredity and Evolution - P143 - Q2
How does the creation of variations in a species promote survival?
Chap 9 - Heredity and Evolution - P147 - Q1
How do Mendel’s experiments show that traits may be dominant or recessive?
Chap 9 - Heredity and Evolution - P147 - Q2
How do Mendel’s experiments show that traits are inheritedindependently?
Chap 9 - Heredity and Evolution - P147 - Q3
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits − blood group A or O − is dominant? Why or why not?
Chap 9 - Heredity and Evolution - P147 - Q4
How is the sex of the child determined in human beings?
Chap 9 - Heredity and Evolution - P150 - Q1
What are the different ways in which individuals with a particular trait may increase in a population?
Chap 9 - Heredity and Evolution - P150 - Q2
Why are traits acquired during the life-time of an individual not inherited?
Chap 9 - Heredity and Evolution - P150 - Q3
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Chap 9 - Heredity and Evolution - P151 - Q1
What factors could lead to the rise of a new species?
Chap 9 - Heredity and Evolution - P151 - Q2
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Chap 9 - Heredity and Evolution - P151 - Q3
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Chap 9 - Heredity and Evolution - P156 - Q1
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Chap 9 - Heredity and Evolution - P156 - Q2
Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Chap 9 - Heredity and Evolution - P156 - Q3
What are fossils? What do they tell us about the process of evolution?
Chap 9 - Heredity and Evolution - P158 - Q1
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Chap 9 - Heredity and Evolution - P158 - Q2
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Chap 9 - Heredity and Evolution - P159 - Q1
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Chap 9 - Heredity and Evolution - P159 - Q2
An example of homologous organs is
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.
Chap 9 - Heredity and Evolution - P159 - Q3
In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
Chap 9 - Heredity and Evolution - P159 - Q4
A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Chap 9 - Heredity and Evolution - P159 - Q5
How are the areas of study − evolution and classification − interlinked?
Chap 9 - Heredity and Evolution - P159 - Q6
Explain the terms analogous and homologous organs with examples.
Chap 9 - Heredity and Evolution - P159 - Q7
Outline a project which aims to find the dominant coat colour in dogs.
Chap 9 - Heredity and Evolution - P159 - Q8
Explain the importance of fossils in deciding evolutionary relationships.
Chap 9 - Heredity and Evolution - P159 - Q9
What evidence do we have for the origin of life from inanimate matter?
Chap 9 - Heredity and Evolution - P159 - Q10
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Chap 9 - Heredity and Evolution - P159 - Q11
How is the equal genetic contribution of male and female parents ensured in the progeny?
Chap 10 - Light – Reflection and Refraction
Chap 10 - Light – Reflection and Refraction - P168 - Q1
Define the principal focus of a concave mirror
Concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.
Chap 10 - Light – Reflection and Refraction - P168 - Q2
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Radius of curvature, R = 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given spherical mirror is 10 cm.
Chap 10 - Light – Reflection and Refraction - P168 - Q3
Name the mirror that can give an erect and enlarged image of an object.
concave mirror, is the image formed is virtual, erect, and enlarged.
Chap 10 - Light – Reflection and Refraction - P168 - Q4
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
It is preferred as a rear-view mirror in vehicles because they give a wider field of view, which allows the driver to see most of the traffic behind him.
Chap 10 - Light – Reflection and Refraction - P171 - Q1
Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Radius of curvature, R = 32 cm
Radius of curvature = 2 × Focal length (f)
R = 2f
Hence, the focal length of the given convex mirror is 16 cm.
Chap 10 - Light – Reflection and Refraction - P171 - Q2
A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?
Let the height of the object, ho = h
Then, height of the image, hI = −3h (Image formed is real)
Object distance, u = −10 cm
v = 3 × (−10) = −30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.
Chap 10 - Light – Reflection and Refraction - P176 - Q1
A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
The light ray bends towards the normal.
water is optically denser than air, a ray of light travelling from air into the water will bend towards the normal.
Chap 10 - Light – Reflection and Refraction - P176 - Q2
Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s−1.
Speed of light in vacuum, c = 3 × 108 m s−1
Refractive index of glass, ng = 1.50
Speed of light in the glass,
Chap 10 - Light – Reflection and Refraction - P176 - Q3
Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.
|
Material medium |
Refractive index |
Material medium |
Refractive index |
|
Air |
1.0003 |
Canada Balsam |
1.53 |
|
Ice |
1.31 |
- |
- |
|
Water |
1.33 |
Rock salt |
1.54 |
|
Alcohol |
1.36 |
- |
- |
|
Kerosene |
1.44 |
Carbon disulphide |
1.63 |
|
Fused quartz |
1.46 |
Dense flint glass |
1.65 |
|
Turpentine oil |
1.47 |
Ruby |
1.71 |
|
Benzene |
1.50 |
Sapphire |
1.77 |
|
Crown glass |
1.52 |
Diamond |
2.42 |
A medium which has the highest refractive index will have the highest optical density and vice-versa.
diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical density.
Chap 10 - Light – Reflection and Refraction - P176 - Q4
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.
|
Material medium |
Refractive index |
Material medium |
Refractive index |
|
Air |
1.0003 |
Canada Balsam |
1.53 |
|
Ice |
1.31 |
- |
- |
|
Water |
1.33 |
Rock salt |
1.54 |
|
Alcohol |
1.36 |
- |
- |
|
Kerosene |
1.44 |
Carbon disulphide |
1.63 |
|
Fused quartz |
1.46 |
Dense flint glass |
1.65 |
|
Turpentine oil |
1.47 |
Ruby |
1.71 |
|
Benzene |
1.50 |
Sapphire |
1.77 |
|
Crown glass |
1.52 |
Diamond |
2.42 |
It can be inferred from the relation that light will travel the slowest in the material which has the highest refractive index and travel the fastest in the material which has the lowest refractive index.
It can be observed from table 10.3 that the refractive indices of kerosene, turpentine, and water are 1.44, 1.47, and 1.33 respectively. Therefore, light travels the fastest in water.
Chap 10 - Light – Reflection and Refraction - P176 - Q5
The refractive index of diamond is 2.42. What is the meaning of this statement?
Where, c is the speed of light in vacuum/air
The refractive index of diamond is 2.42. This suggests that the speed of light in diamond will reduce by a factor 2.42 compared to its speed in air.
Chap 10 - Light – Reflection and Refraction - P184 - Q1
Define 1 dioptre of power of a lens.
The S.I. unit of power of a lens is Dioptre. It is denoted by D.
1 dioptre is defined as the power of a lens of focal length 1 metre.
∴1 D = 1 m−1
Chap 10 - Light – Reflection and Refraction - P184 - Q2
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of
50 cm.
Object distance, u = −50 cm
Image distance, v = 50 cm
Focal length = f
According to the lens formula,
Hence, the power of the given lens is +4 D.
Chap 10 - Light – Reflection and Refraction - P184 - Q3
Find the power of a concave lens of focal length 2 m.
Focal length of concave lens, f = 2 m
Here, negative sign arises due to the divergent nature of concave lens.
Hence, the power of the given concave lens is −0.5 D.
Chap 10 - Light – Reflection and Refraction - P185 - Q1
Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
(d) Clay
Chap 10 - Light – Reflection and Refraction - P185 - Q2
The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.
(d) Between the pole of the mirror and its principal focus.
Chap 10 - Light – Reflection and Refraction - P185 - Q3
Where should an object be placed in front of a convex lens to get a real image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus.
(b) At twice the focal length
Chap 10 - Light – Reflection and Refraction - P185 - Q4
A spherical mirror and a thin spherical lens have each a focal length of −15 cm. The mirror and the lens are likely to be
(a) both concave
(b) both convex
(c) the mirror is concave and the lens is convex
(d) the mirror is convex, but the lens is concave
(a) both concave
Chap 10 - Light – Reflection and Refraction - P186 - Q5
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex
(d) either plane or convex
Chap 10 - Light – Reflection and Refraction - P186 - Q6
Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm
(c) A convex lens of focal length 5 cm
Chap 10 - Light – Reflection and Refraction - P186 - Q7
We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.
A concave mirror gives an erect image when an object is placed between its pole (P) and the principal focus (F).
Hence, to obtain an erect image of an object from a concave mirror of focal length 15 cm, the object must be placed anywhere between the pole and the focus. The image formed will be virtual, erect, and magnified in nature
Chap 10 - Light – Reflection and Refraction - P186 - Q8
Name the type of mirror used in the following situations.
(a) Headlights of a car
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace
Support your answer with reason.
(a) Concave (b) Convex (c) Concave
Explanation
(a) Concave mirror is used in the headlights of a car. This is because concave mirrors can produce powerful parallel beam of light when the light source is placed at their principal focus.
(b) Convex mirror is used in side/rear view mirror of a vehicle. Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of it. Because of this, they have a wide field of view. It enables the driver to see most of the traffic behind him/her.
(c) Concave mirrors are convergent mirrors. That is why they are used to construct solar furnaces. Concave mirrors converge the light incident on them at a single point known as principal focus. Hence, they can be used to produce a large amount of heat at that point.
Chap 10 - Light – Reflection and Refraction - P186 - Q9
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
The convex lens will form complete image of an object, even if its one half is covered with black paper. It can be understood by the following two cases.
Case I
When the upper half of the lens is covered
In this case, a ray of light coming from the object will be refracted by the lower half of the lens. These rays meet at the other side of the lens to form the image of the given object.
Case II
When the lower half of the lens is covered
In this case, a ray of light coming from the object is refracted by the upper half of the lens. These rays meet at the other side of the lens to form the image of the given object.
Chap 10 - Light – Reflection and Refraction - P186 - Q10
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
According to the lens formula,
The positive value of v shows that the image is formed at the other side of the lens.
The negative sign shows that the image is real and formed behind the lens.
The negative value of image height indicates that the image formed is inverted.
Chap 10 - Light – Reflection and Refraction - P186 - Q11
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
According to the lens formula,
The negative value of u indicates that the object is placed 30 cm in front of the lens.
Chap 10 - Light – Reflection and Refraction - P186 - Q12
An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
According to the mirror formula,
v
The positive value of v indicates that the image is formed behind the mirror.
The positive value of magnification indicates that the image formed is virtual and erect.
Chap 10 - Light – Reflection and Refraction - P186 - Q13
The magnification produced by a plane mirror is +1. What does this mean?
The magnification produced by a plane mirror is +1. It shows that the image formed by the plane mirror is of the same size as that of the object. The positive sign shows that the image formed is virtual and erect.
Chap 10 - Light – Reflection and Refraction - P186 - Q14
An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size
According to the mirror formula,
The positive value of v indicates that the image is formed behind the mirror.
The positive value of image height indicates that the image formed is erect.
Therefore, the image formed is virtual, erect, and smaller in size.
Chap 10 - Light – Reflection and Refraction - P186 - Q15
An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.
According to the mirror formula,
The screen should be placed at a distance of 54 cm in front of the given mirror.
The negative value of magnification indicates that the image formed is real.
The negative value of image height indicates that the image formed is inverted.
Chap 10 - Light – Reflection and Refraction - P186 - Q16
Find the focal length of a lens of power −2.0 D. What type of lens is this?
A concave lens has a negative focal length. Hence, it is a concave lens.
Chap 10 - Light – Reflection and Refraction - P186 - Q17
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
A convex lens has a positive focal length. Hence, it is a convex lens or a converging lens
Chap 11 - Human Eye and Colourful World
Chap 11 - Human Eye and Colourful World - P190 - Q1
What is meant by power of accommodation of the eye?
The ciliary muscles contract making the eye lens thicker. Thus, the focal length of the eye lens decreases and the nearby objects become visible to the eyes. Hence, the human eye lens is able to adjust its focal length to view both distant and nearby objects on the retina. This ability is called the power of accommodation of the eyes.
Chap 11 - Human Eye and Colourful World - P190 - Q2
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Because the image of an object beyond 1.2 m is formed in front of the retina and not at the retina, as shown in the given figure.
To correct this defect of vision, he must use a concave lens. The concave lens will bring the image back to the retina as shown in the given figure.
Chap 11 - Human Eye and Colourful World - P190 - Q3
What is the far point and near point of the human eye with normal vision?
The minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm. is called near point of the human eye.
The maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity is called the far point of the eye.
Chap 11 - Human Eye and Colourful World - P190 - Q4
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
It shows that he is unable to see distant objects clearly. He is suffering from myopia. This defect can be corrected by using a concave lens.
Chap 11 - Human Eye and Colourful World - P197 - Q1
The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to
(a) presbyopia
(b) accommodation
(c) near-sightedness
(d) far-sightedness
(b) accommodation
Chap 11 - Human Eye and Colourful World - P198 - Q2
The human eye forms the image of an object at its
(a) cornea (b) iris (c) pupil (d) retina
(d) retina
Chap 11 - Human Eye and Colourful World - P198 - Q3
The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m
(b) 2.5 cm
(c) 25 cm
(d) 2.5 m
(c) 25 cm
Chap 11 - Human Eye and Colourful World - P198 - Q4
The change in focal length of an eye lens is caused by the action of the
(a) pupil
(b) retina
(c) ciliary muscles
(d) iris
(c) ciliary muscles
Chap 11 - Human Eye and Colourful World - P198 - Q5
A person needs a lens of power −5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
For distant vision = −0.181 m, for near vision = 0.667 m
The power P of a lens of focal length f is given by the relation
(i) Power of the lens used for correcting distant vision = −5.5 D
Focal length of the required lens, f =
The focal length of the lens for correcting distant vision is −0.181 m.
(ii) Power of the lens used for correcting near vision = +1.5 D
Focal length of the required lens, f =
The focal length of the lens for correcting near vision is 0.667 m.
Chap 11 - Human Eye and Colourful World - P198 - Q6
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
The convex lens actually creates a virtual image of a nearby object (N’ in the figure) at the near point of vision (N) of the person suffering from hypermetropia.
The given person will be able to clearly see the object kept at 25 cm (near point of the normal eye), if the image of the object is formed at his near point, which is given as 1 m.
Object distance, u = −25 cm
Image distance, v = −1 m = −100 m
Focal length, f
Using the lens formula,
A convex lens of power +3.0 D is required to correct the defect.
Chap 11 - Human Eye and Colourful World - P198 - Q7
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit.
If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.
Chap 11 - Human Eye and Colourful World - P198 - Q8
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.
Chap 11 - Human Eye and Colourful World - P198 - Q9
What happens to the image distance in the eye when we increase the distance of an object from the eye?
When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change in the focal length of the eye lens. The focal length of the eyes changes in such a way that the image is always formed at the retina of the eye
Chap 11 - Human Eye and Colourful World - P198 - Q10
Why do stars twinkle?
When the light coming from stars enters the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of the atmosphere. When the star light refracted by the atmosphere comes more towards us, it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night.
Chap 11 - Human Eye and Colourful World - P198 - Q11
Explain why the planets do not twinkle?
The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.
Chap 11 - Human Eye and Colourful World - P198 - Q12
Why does the Sun appear reddish early in the morning?
Blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore, the Sun appears reddish early in the morning.
Chap 11 - Human Eye and Colourful World - P198 - Q13
Why does the sky appear dark instead of blue to an astronaut?
There is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to them.
Chap 12 - Electricity
Chap 12 - Electricity - P200 - Q1
What does an electric circuit mean?
A switch makes a conducting link between the cell and the bulb. A continuous and closed path of an electric current is called an electric circuit.
Chap 12 - Electricity - P200 - Q2
Define the unit of current.
The electric current is expressed by a unit called ampere (A), One ampere is
constituted by the flow of one coulomb of charge per second,
Chap 12 - Electricity - P200 - Q3
Calculate the number of electrons constituting one coulomb of charge.
1 electron possesses a charge of 1.6 × 10−19 C, i.e., 1.6 × 10−19 C of charge is contained in 1 electron.
∴ 1 C of charge is contained in
Therefore, electrons constitute one coulomb of charge.
Chap 12 - Electricity - P202 - Q1
Name a device that helps to maintain a potential difference across a conductor.
cell, battery, power supply, etc. helps to maintain a potential difference across a conductor.
Chap 12 - Electricity - P202 - Q2
What is meant by saying that the potential difference between two points is 1 V?
If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.
Chap 12 - Electricity - P202 - Q3
How much energy is given to each coulomb of charge passing through a 6 V battery?
Energy given to each coulomb of charge is equal to the amount of work required to move it. The amount of work is given by the expression,
Potential difference =
Where,
Charge = 1 C
Potential difference = 6 V
Therefore, 6 J of energy is given to each coulomb of charge passing through a battery of 6 V.
Chap 12 - Electricity - P209 - Q1
On what factors does the resistance of a conductor depend?
The resistance of the conductor depends (i) on its length, (ii) on its area of cross-section, and (iii) on the nature of its material. Precise measurements have shown that resistance of a uniform metallic conductor is directly proportional to its length
Chap 12 - Electricity - P209 - Q2
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Resistance of a wire,
Where,
= Resistivity of the material of the wire
l = Length of the wire
A = Area of cross-section of the wire
Resistance is inversely proportional to the area of cross-section of the wire.
Thicker the wire, lower is the resistance of the wire and vice-versa. Therefore, current can flow more easily through a thick wire than a thin wire.
Chap 12 - Electricity - P209 - Q3
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
According to Ohm’s law
V = IR
Where,
Resistance of the electrical component = R
Potential difference = V
Current = I
The potential difference is reduced to half, keeping resistance constant.
Let the new resistance be R' and the new amount of current be I '.
Therefore, from Ohm’s law, we obtain the amount of new current.
Therefore, the amount of current flowing through the electrical component is reduced by half.
Chap 12 - Electricity - P209 - Q4
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Because an alloy is higher than the pure metal. Moreover, at high temperatures, the alloys do not melt readily.
Chap 12 - Electricity - P209 - Q5
Use the data in Table 12.2 to answer the following −
Table 12.2 Electrical resistivity of some substances at 20°C
|
− |
Material |
Resistivity (Ω m) |
|
Conductors |
Silver |
1.60 × 10−8 |
|
Copper |
1.62 × 10−8 |
|
|
Aluminium |
2.63 × 10−8 |
|
|
Tungsten |
5.20 × 10−8 |
|
|
Nickel |
6.84 × 10−8 |
|
|
Iron |
10.0 × 10−8 |
|
|
Chromium |
12.9 × 10−8 |
|
|
Mercury |
94.0 × 10−8 |
|
|
Manganese |
1.84 × 10−6 |
|
|
Constantan (alloy of Cu and Ni) |
49 × 10−6 |
|
|
Alloys |
Manganin (alloy of Cu, Mn and Ni) |
44 × 10−6 |
|
Nichrome (alloy of Ni, Cr, Mn and Fe) |
100 × 10−6 |
|
|
Glass |
1010 − 1014 |
|
|
Insulators |
Hard rubber |
1013 − 1016 |
|
Ebonite |
1015 − 1017 |
|
|
Diamond |
1012 − 1013 |
|
|
Paper (dry) |
1012 |
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
a) Resistivity of iron =
Resistivity of mercury =
Resistivity of mercury is more than that of iron. This implies that iron is a better conductor than mercury.
(b) It can be observed from Table 12.2 that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.
Chap 12 - Electricity - P213 - Q1
Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.
Three cells of potential 2 V, each prescribed in series, is equivalent to a battery of potential 2 V + 2 V + 2 V = 6V.
The following circuit diagram shows three resistors of resistances 5 Ω, 8 Ω and 12 Ω respectively connected in series and a battery of potential 6 V.
Chap 12 - Electricity - P213 - Q2
Redraw the circuit of question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter?
To calculate the current flowing through the resistors, an ammeter should be connected in the circuit in series with the resistors. To measure the potential difference across the 12 Ω resistor, a voltmeter should be connected parallel to this resistor, as shown in the following figure.
The resistances are connected in series.
Ohm’s law can be used to obtain the readings of ammeter and voltmeter. According to Ohm’s law,
V = IR,
Where,
Potential difference, V = 6 V
Current flowing through the circuit/resistors = I
Resistance of the circuit, R =
= 0.24 A
Potential difference across 12 Ω resistor =
Current flowing through the 12 Ω resistor, I = 0.24 A
Therefore, using Ohm’s law, we obtain
Therefore, the reading of the ammeter will be 0.24 A.
The reading of the voltmeter will be 2.88 V.
Chap 12 - Electricity - P216 - Q1
Judge the equivalent resistance when the following are connected in parallel − (a) 16Ω and 106Ω, (b) 16Ω and 103Ω and 106Ω.
(a) When 1 Ω and 106 Ω are connected in parallel:
Let R be the equivalent resistance.
Therefore, equivalent resistance 1 Ω
(b) When 1 Ω, , and
are connected in parallel:
Let R be the equivalent resistance.
Therefore, equivalent resistance = 0.999 Ω
Chap 12 - Electricity - P216 - Q2
An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?
Resistance of electric lamp,
Resistance of toaster,
Resistance of water filter,
Voltage of the source, V = 220 V
These are connected in parallel, as shown in the following figure.
Let R be the equivalent resistance of the circuit.
According to Ohm’s law,
V = IR
Where,
Current flowing through the circuit = I
7.04 A of current is drawn by all the three given appliances.
Therefore, current drawn by an electric iron connected to the same source of potential 220 V = 7.04 A
Let be the resistance of the electric iron. According to Ohm’s law,
Therefore, the resistance of the electric iron is and the current flowing through it is 7.04 A.
Chap 12 - Electricity - P216 - Q3
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
The potential difference across each appliance is equal to the supplied voltage.
The total effective resistance of the circuit can be reduced by connecting electrical appliances in parallel
Chap 12 - Electricity - P216 - Q4
How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?
There are three resistors of resistances 2 Ω, 3 Ω, and 6 Ω respectively.
(a) The following circuit diagram shows the connection of the three resistors.
Here, 6 Ω and 3 Ω resistors are connected in parallel.
Therefore, their equivalent resistance will be given by
This equivalent resistor of resistance 2 Ω is connected to a 2 Ω resistor in series.
Therefore, equivalent resistance of the circuit = 2 Ω + 2 Ω =
Hence, the total resistance of the circuit is .
2. The following circuit diagram shows the connection of the three resistors.
All the resistors are connected in series. Therefore, their equivalent resistance will be given as
Therefore, the total resistance of the circuit is .
Chap 12 - Electricity - P216 - Q5
What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
There are four coils of resistances , 12 Ω, and 24 Ω respectively.
(a) If these coils are connected in series, then the equivalent resistance will be the highest, given by the sum 4 + 8 + 12 + 24 =
(b) If these coils are connected in parallel, then the equivalent resistance will be the lowest, given by
Therefore, 2 Ω is the lowest total resistance
Chap 12 - Electricity - P218 - Q1
Why does the cord of an electric heater not glow while the heating element does?
Because of the amount of heat produced by it is proportional to its resistance. The resistance of the element of an electric heater is very high
Chap 12 - Electricity - P218 - Q2
Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.
The amount of heat (H) produced is given by the Joule’s law of heating as
Where,
Voltage, V = 50 V
Time, t = 1 h = 1 × 60 × 60 s
Amount of current,
Therefore, the heat generated is .
Chap 12 - Electricity - P218 - Q3
An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
The amount of heat (H) produced is given by the joule’s law of heating as
Where,
Current, I = 5 A
Time, t = 30 s
Voltage, V = Current × Resistance = 5 × 20 = 100 V
Therefore, the amount of heat developed in the electric iron is
Chap 12 - Electricity - P220 - Q1
What determines the rate at which energy is delivered by a current?
The rate of consumption of electric energy in an electric appliance is called electric power
Chap 12 - Electricity - P220 - Q2
An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.
Power (P) is given by the expression,
Where,
Voltage, V = 220 V
Current, I = 5 A
Energy consumed by the motor = Pt
Where,
Time, t = 2 h = 2 × 60 × 60 = 7200 s
P = 1100 × 7200 = 7.92 × 106 J
Therefore, power of the motor = 1100 W
Energy consumed by the motor = 7.92 × 106 J
Chap 12 - Electricity - P221 - Q1
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is −
(d) Resistance of a piece of wire is proportional to its length. A piece of wire has a resistance R. The wire is cut into five equal parts.
Therefore, resistance of each part =
All the five parts are connected in parallel. Hence, equivalent resistance (R’) is given as
Therefore, the ratio is 25.
Chap 12 - Electricity - P221 - Q2
Which of the following terms does not represent electrical power in a circuit?
(a) I2R
(b) IR2
(c) VI
(d) v2/r
(b) IR2
Chap 12 - Electricity - P221 - Q3
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be −
(d) 25 W
Chap 12 - Electricity - P221 - Q4
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be −
(a) 1:2
(b) 2:1
(c) 1:4
(d) 4:1
(c) 1:4
Chap 12 - Electricity - P221 - Q5
How is a voltmeter connected in the circuit to measure the potential difference between two points?
A voltmeter should be connected in parallel to the points
Chap 12 - Electricity - P221 - Q6
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8 Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?
Resistance (R) of a copper wire of length l and cross-section A is given by the expression,
Where,
Resistivity of copper,
Area of cross-section of the wire, A =
Diameter= 0.5 mm = 0.0005 m
Resistance, R = 10 Ω
Hence, length of the wire,
If the diameter of the wire is doubled, new diameter
Therefore, resistance
Therefore, the length of the wire is 122.7 m and the new resistance is
Chap 12 - Electricity - P221 - Q7
The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below −
The slope of the line gives the value of resistance (R) as,
Therefore, the resistance of the resistor is .
Chap 12 - Electricity - P221 - Q8
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Resistance (R) of a resistor is given by Ohm’s law as,
Where,
Potential difference, V = 12 V
Current in the circuit, I = 2.5 mA =
Therefore, the resistance of the resistor is
Chap 12 - Electricity - P221 - Q9
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
There is no current division occurring in a series circuit. Current flow through the component is the same, given by Ohm’s law as
Where,
R is the equivalent resistance of resistances .
0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω, and12 Ω These are connected in series. Hence, the sum of the resistances will give the value of R.
R = 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4 Ω
Potential difference, V = 9 V
Therefore, the current that would flow through the 12 Ω resistor is 0.671 A.
Chap 12 - Electricity - P221 - Q10
How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
For x number of resistors of resistance 176 Ω, the equivalent resistance of the resistors connected in parallel is given by Ohm’s law as
Where,
Supply voltage, V = 220 V
Current, I = 5 A
Equivalent resistance of the combination = R,given as
From Ohm’s law,
Therefore, four resistors of 176 Ω are required to draw the given amount of current
Chap 12 - Electricity - P221 - Q11
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
If we joints the resistors in series, then the equivalent resistance will be the sum of the resistors, i.e., 6 Ω + 6 Ω + 6 Ω = 18 Ω, which is not desired. If we connect the resistors in parallel, then the equivalent resistance will be
Hence, we should either connect the two resistors in series or parallel.
(i) Two resistors in parallel
Two 6 Ω resistors are connected in parallel. Their equivalent resistance will be
The third 6 Ω resistor is in series with 3 Ω. Hence, the equivalent resistance of the circuit is 6 Ω + 3 Ω = 9 Ω.
(ii) Two resistors in series
Two 6 Ω resistors are in series. Their equivalent resistance will be the sum
The third 6 Ω resistor is in parallel with 12 Ω. Hence, equivalent resistance will be
Therefore, the total resistance is .
Chap 12 - Electricity - P221 - Q12
Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?
Resistance R1 of the bulb is given by the expression,
Where,
Supply voltage, V = 220 V
Maximum allowable current, I = 5 A
Rating of an electric bulb
According to Ohm’s law,
V = I R
Where,
R is the total resistance of the circuit for x number of electric bulbs
Resistance of each electric bulb,
Therefore, 110 electric bulbs are connected in parallel
Chap 12 - Electricity - P221 - Q13
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?
Supply voltage, V = 220 V
Resistance of one coil, R =
(i) Coils are used separately
According to Ohm’s law,
Where,
is the current flowing through the coil
Therefore, 9.16 A current will flow through the coil when used separately.
(ii) Coils are connected in series
Total resistance,
According to Ohm’s law,
Where,
is the current flowing through the series circuit
Therefore, 4.58 A current will flow through the circuit when the coils are connected in series.
(iii) Coils are connected in parallel
Total resistance, is given as
According to Ohm’s law,
Where,
is the current flowing through the circuit
Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.
Chap 12 - Electricity - P221 - Q14
Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
(i) Potential difference, V = 6 V
1 Ω and 2 Ω resistors are connected in series. Therefore, equivalent resistance of the circuit, R = 1 + 2 = 3 Ω
According to Ohm’s law,
V = IR
Where,
I is the current through the circuit
This current will flow through each component of the circuit because there is no division of current in series circuits. Hence, current flowing through the 2 Ω resistor is . Power is given by the expression,
(ii) Potential difference, V = 4 V
12 Ω and 2 Ω resistors are connected in parallel. The voltage across each component of a parallel circuit remains the same. Hence, the voltage across 2 Ω resistor will be 4 V.
Power consumed by 2 Ω resistor is given by
Therefore, the power used by 2 Ω resistor is 8 W.
Chap 12 - Electricity - P222 - Q15
Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage occurs in a parallel circuit.
Current drawn by the bulb of rating 100 W is given by,
Similarly, current drawn by the bulb of rating 100 W is given by,
Chap 12 - Electricity - P222 - Q16
Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Energy consumed by an electrical appliance is given by the expression,
Where,
Power of the appliance = P
Time = t
Energy consumed by a TV set of power 250 W in 1 h = 250 × 3600 = 9 × 105 J
Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 × 600
= 7.2× 105 J
Therefore, the energy consumed by a 250 W TV set in 1 h is more than the energy consumed by a toaster of power 1200 W in 10 minutes.
Chap 12 - Electricity - P222 - Q17
An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.
Rate of heat produced by a device is given by the expression for power as
Where,
Resistance of the electric heater, R = 8 Ω
Current drawn, I = 15 A
Therefore, heat is produced by the heater at the rate of 1800 J/s.
Chap 12 - Electricity - P222 - Q18
Explain the following.
(a) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?
(a) The melting point of tungsten are very high. It does not burn readily at a high temperature. The electric lamps glow at very high temperatures. Hence, tungsten is mainly used as heating element of electric bulbs.
(b) The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of metals. It produces large amount of heat.
(c) A component of a series circuit receives a small voltage for a large supply voltage. As a result, the amount of current decreases and the device becomes hot. Hence, series arrangement is not used in domestic circuits.
(d) Resistance (R) of a wire is inversely proportional to its area of cross-section (A), i.e.,
(e) Copper and aluminium wires have low resistivity. They are good conductors of electricity.
Chap 13 - Magnetic Effects of Electric Current
Chap 13 - Magnetic Effects of Electric Current - P224 - Q1
Why does a compass needle get deflected when brought near a bar magnet?
A compass needle shows a deflection when brought near the bar magnet, because a compass needle is a small bar magnet. When it is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet.
Chap 13 - Magnetic Effects of Electric Current - P228 - Q1
Draw magnetic field lines around a bar magnet.
Chap 13 - Magnetic Effects of Electric Current - P228 - Q2
List the properties of magnetic lines of force.
The properties of magnetic lines of force are as follows.
(a) Magnetic field lines emerge from the north pole.
(b) They merge at the south pole.
(c) The direction of field lines inside the magnet is from the south pole to the north pole.
(d) Magnetic lines do not intersect with each other.
Chap 13 - Magnetic Effects of Electric Current - P228 - Q3
Why don’t two magnetic lines of force intersect each other?
If two field lines of a magnet intersect, then at the point of intersection, the compass needle points in two different directions. This is not possible. Hence, two field lines do not intersect each other.
Chap 13 - Magnetic Effects of Electric Current - P229 - Q1
Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop,
Chap 13 - Magnetic Effects of Electric Current - P229 - Q2
The magnetic field in a given region is uniform. Draw a diagram to represent it.
Chap 13 - Magnetic Effects of Electric Current - P230 - Q3
Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a) is zero
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points
(d)The magnetic field inside a long, straight, current-carrying solenoid is uniform. It is the same at all points inside the solenoid.
Chap 13 - Magnetic Effects of Electric Current - P231 - Q1
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
(c) and (d)
Chap 13 - Magnetic Effects of Electric Current - P232 - Q2
In Activity 13.7 (page: 230), how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?
A current-carrying conductor placed in a magnetic field experiences a force. The magnitude of force increases with the amount of current, strength of the magnetic field, and the length of the conductor. Hence, the magnetic force exerted on rod AB and its deflection will increase if
(i) current in rod AB is increased
(ii) a stronger horse-shoe magnet is used
(iii) length of rod AB is increased
Working...
Chap 13 - Magnetic Effects of Electric Current - P232 - Q3
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south (b) towards east
(c) downward (d) upward
(d) upward
Chap 13 - Magnetic Effects of Electric Current - P233 - Q1
State Fleming’s left-hand rule.
Fleming’s left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.
Chap 13 - Magnetic Effects of Electric Current - P233 - Q2
What is the principle of an electric motor?
A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is given by the Fleming’s left-hand rule.
Chap 13 - Magnetic Effects of Electric Current - P233 - Q3
What is the role of the split ring in an electric motor?
The commutator reverses the direction of current flowing through the coil after each half rotation of the coil. Due to this reversal of the current, the coil continues to rotate in the same direction.
Chap 13 - Magnetic Effects of Electric Current - P236 - Q1
Explain different ways to induce current in a coil.
The different ways to induce current in a coil are as follows:
(a) If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
(b) If a magnet is moved relative to a coil, then an electric current is induced in the coil.
Chap 13 - Magnetic Effects of Electric Current - P237 - Q1
State the principle of an electric generator.
An electric generator works on the principle of electromagnetic induction. It generates electricity by rotating a coil in a magnetic field.
Chap 13 - Magnetic Effects of Electric Current - P237 - Q2
Name some sources of direct current.
Some sources of direct current are cell, DC generator, etc.
Chap 13 - Magnetic Effects of Electric Current - P237 - Q3
Which sources produce alternating current?
AC generators, power plants, etc., produce alternating current.
Chap 13 - Magnetic Effects of Electric Current - P237 - Q4
Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
(c) half revolution
Chap 13 - Magnetic Effects of Electric Current - P238 - Q1
Name two safety measures commonly used in electric circuits and appliances.
Two safety measures commonly used in electric circuits and appliances are as follows:
(i) When the current passing through the wire exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current through that circuit, hence protecting the appliances connected to the circuit.
(ii) Any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.
Chap 13 - Magnetic Effects of Electric Current - P238 - Q2
An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Current drawn by the electric oven can be obtained by the expression,
P = VI
Where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.
Chap 13 - Magnetic Effects of Electric Current - P238 - Q3
What precaution should be taken to avoid the overloading of domestic electric circuits?
The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
(a) Faulty appliances should not be connected in the circuit.
(b) Fuse should be connected in the circuit.
Chap 13 - Magnetic Effects of Electric Current - P240 - Q1
Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centred on the wire
(d) The field consists of concentric circles centred on the wire
Chap 13 - Magnetic Effects of Electric Current - P240 - Q2
The phenomenon of electromagnetic induction is
(a) the process of charging a body
(b) the process of generating magnetic field due to a current passing through a coil
(c) producing induced current in a coil due to relative motion between a magnet and the coil
(d) the process of rotating a coil of an electric motor
(c) producing induced current in a coil due to relative motion between a magnet and the coil
Chap 13 - Magnetic Effects of Electric Current - P240 - Q3
The device used for producing electric current is called a
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
(a) generator
Chap 13 - Magnetic Effects of Electric Current - P240 - Q4
The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
(d) AC generator has slip rings while the DC generator has a commutator.
Chap 13 - Magnetic Effects of Electric Current - P240 - Q5
At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously
(c) increases heavily
Chap 13 - Magnetic Effects of Electric Current - P240 - Q6
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
(a) False
(b) True
(c) True
(d) False
Chap 13 - Magnetic Effects of Electric Current - P240 - Q7
List three sources of magnetic fields.
Three sources of magnetic fields are as follows:
(a) Current-carrying conductors
(b) Permanent magnets
(c) Electromagnets
Chap 13 - Magnetic Effects of Electric Current - P241 - Q8
How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q9
When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
when the direction of current is perpendicular to the direction of the magnetic field.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q10
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
The direction of current is from the front wall to the back wall because negatively charged electrons are moving from back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q11
Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.
Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming’s left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise.
After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q12
Name some devices in which electric motors are used?
Some devices in which electric motors are used are as follows:
(a) Water pumps
(b) Electric fans
(c) Electric mixers
(d) Washing machines
Chap 13 - Magnetic Effects of Electric Current - P241 - Q13
A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
A current induces in a solenoid if a bar magnet is moved relative to it. This is the principle of electromagnetic induction.
(i) A current is induced momentarily in the coil. As a result, the needle of the galvanometer deflects momentarily in a particular direction.
(ii) The needle of the galvanometer deflects momentarily in the opposite direction.
(iii) galvanometer will show no deflection.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q14
Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Two circular coils A and B are placed close to each other. When the current in coil A is changed, the magnetic field associated with it also changes. As a result, the magnetic field around coil B also changes. This change in magnetic field lines around coil B induces an electric current in it. This is called electromagnetic induction.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q15
State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
(i) Maxwell’s right hand thumb rule
(ii) Fleming’s left hand rule
(iii) Fleming’s right hand rule
Chap 13 - Magnetic Effects of Electric Current - P241 - Q16
Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
An electric generator converts mechanical energy into electrical energy.
The principle of working of an electric generator is that when a loop is moved in a magnetic field, an electric current is induced in the coil. It generates electricity by rotating a coil in a magnetic field. The following figure shows a simple AC generator.
The direction of current in the coil is MNST. Hence, the galvanometer shows a deflection in a particular direction. After half a rotation, length MN starts moving down whereas length ST starts moving upward. The direction of the induced current in the coil gets reversed as TSNM. As the direction of current gets reversed after each half rotation, the produced current is called an alternating current (AC).
To get a unidirectional current, instead of two slip rings, two split rings are used, as shown in the following figure.
In this arrangement, brush A always remains in contact with the length of the coil that is moving up whereas brush B always remains in contact with the length that is moving down. The split rings C and D act as a commutator.
The direction of current induced in the coil will be MNST for the first rotation and TSNM in the second half of the rotation. Hence, a unidirectional current is produced from the generator called DC generator. The current is called AC current.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q17
When does an electric short circuit occur?
When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly. Hence, a short circuit occurs.
Chap 13 - Magnetic Effects of Electric Current - P241 - Q18
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.
Chap 14 - Sources of Energy
Chap 14 - Sources of Energy - P243 - Q1
What is a good source of energy?
In our daily lives, use energy from various sources for doing work. We use diesel to run our trains. We use electricity to light our street-lamps. Or we use energy in our muscles to cycle to school.
Chap 14 - Sources of Energy - P243 - Q2
What is a good fuel?
A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.
Chap 14 - Sources of Energy - P243 - Q3
What is a good fuel?
It is a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.
Chap 14 - Sources of Energy - P248 - Q1
What are the disadvantages of fossil fuels?
1. air pollution caused by burning of coal or petroleum products.
2. The oxides of carbon, nitrogen and sulphur that are released on burning
fossil fuels are acidic oxides. These lead to acid rain which affects our
water and soil resources.
Chap 14 - Sources of Energy - P248 - Q2
Why are we looking at alternate sources of energy?
Because Fossil fuels, which have been traditionally used by human beings as an energy sources, are non-renewable sources of energy. These sources of energy are limited and cannot replenish on their own. They are being consumed at a large rate. If this rate of consumption continues, then the fossil fuels would be exhausted from the Earth.
Chap 14 - Sources of Energy - P248 - Q3
How has the traditional use of wind and water energy been modified for our convenience?
Traditionally, waterfalls were used as a source of Storage body which was converted to electricity with the help of turbines. Since waterfalls are few in number, water dams have been constructed in large numbers. Nowadays, hydro-dams are used in order to harness potential energy of stored water. In water dams, water falls from a height on the turbine, which produces electricity.
Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting/drawing water from a well. Today, windmills are used to generate electricity. In windmills, the kinetic energy of wind is harnessed and converted into electricity. The rotatory motion of the blades turns the turbine of the electric generator to generate electricity.
Chap 14 - Sources of Energy - P253 - Q1
What kind of mirror − concave, convex or plain − would be best suited for use in a solar cooker? Why
A solar cooker uses heat of the sunlight to cook and heat food. A mirror is used in order to reflect and focus sunlight at a point.
A concave mirror is used in a solar cooker for this purpose. The mirror focuses all the incident sunlight at a point. The temperature at that point increases, thereby cooking and heating the food placed at that point.
Chap 14 - Sources of Energy - P253 - Q1
Can any source of energy be pollution-free? Why or why not?
No source of energy can be pollution-free. Because To start the fusion reactions, approximately 107 K temperature is required, which is provided by fission reactions. The wastes released from fission reactions are very hazardous. Hence, no source of energy is pollution-free.
Chap 14 - Sources of Energy - P253 - Q2
What are the limitations of the energy that can be obtained from the oceans?
Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
(ii) High dams are required to be built to convert tidal energy into electricity.
(iii) Very strong waves are required to obtain electricity from wave energy.
(iv) To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20ºC or more.
Chap 14 - Sources of Energy - P253 - Q2
Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Hydrogengas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon contents. Because fusion of hydrogen does not produce any waste.
Chap 14 - Sources of Energy - P253 - Q3
What is geothermal energy?
When underground water comes in contact with the hot spot, steam is generated. Sometimes hot water from that region finds outlets
at the surface. Such outlets are known as hot springs. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity. The cost of production would not be much, but there are very few commercially viable sites where such energy can be exploited.
Chap 14 - Sources of Energy - P253 - Q4
What are the advantages of nuclear energy?
(a) Fusion of four hydrogen atoms produces huge amount of energy approximately equal to 27 MeV.
(b) Large amount of energy is produced per unit mass. Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon.
Chap 14 - Sources of Energy - P254 - Q1
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Bio-Mass
cow-dung, various plant materials like the residue afterharvesting the crops, vegetable waste and sewage are decomposed in
the absence of oxygen to give bio-gas. Since the starting material is mainlycow-dung, it is popularly known as ‘ gobar-gas’.
Wind
To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator. The output of a single windmill is quite small and cannot be used for commercial purposes. Therefore, a number of windmills are erected over a large area, which is known as wind energyfarm.
Chap 14 - Sources of Energy - P254 - Q1
A solar water heater cannot be used to get hot water on
(a) a sunny day (b) a cloudy day
(c) a hot day (d)a windy day
(b) a cloudy day
Chap 14 - Sources of Energy - P254 - Q2
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Two exhaustible energy sources are as follows:
(a) Coal: It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non-renewable or exhaustible source of energy.
(b) Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the Earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.
Chap 14 - Sources of Energy - P255 - Q2
Which of the following is not an example of a bio-mass energy source?
(a) wood
(b) gobar gas
(c) nuclear energy
(d) coal
(c) nuclear energy
Chap 14 - Sources of Energy - P255 - Q3
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Bio-mass
(c) Nuclear energy
Chap 14 - Sources of Energy - P255 - Q4
Compare and contrast fossil fuels and the Sun as direct sources of energy.
Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath the Earth’s crust. They are directly available to human beings for use.
On the other hand, solar energy is a renewable and direct source of energy.Solar energy is available free of cost to all in unlimited amount. It replenishes in the Sun itself
Chap 14 - Sources of Energy - P255 - Q5
Compare and contrast bio-mass and hydro electricity as sources of energy.
Hydro-electricity, on the other hand, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.
Chap 14 - Sources of Energy - P255 - Q6
What are the limitations of extracting energy from −
(a) the wind? (b) waves? (c) tides?
(a) Wind energy is harnessed by windmills. One of the limitations of extracting energy from wind is that a windmill requires wind of speed more than 15 km/h to generate electricity. Also, a large number of windmills are required, which covers a huge area.
(b) Very strong ocean waves are required in order to extract energy from waves.
(c) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.
Chap 14 - Sources of Energy - P255 - Q7
On what basis would you classify energy sources as
(a) renewable and non-renewable?
(b) exhaustible and inexhaustible?
Are the options given in (a) and (b) the same?
(a) The source of energy that replenishes in nature is known as renewable source of energy. Sun, wind, moving water, bio-mass, etc. are some of the examples of renewable sources of energy.
The source of energy that does not replenish in nature is known as non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-renewable sources of energy.
(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.
Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Bio-mass is one of the inexhaustible sources of energy.
Yes. The options given in (a) and (b) are the same.
Chap 14 - Sources of Energy - P255 - Q8
What are the qualities of an ideal source of energy?
An ideal source of energy must be:
I. Economical
II. Easily accessible
III. Smoke/pollution free
Chap 14 - Sources of Energy - P255 - Q9
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy
Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy day, it becomes useless.
Chap 14 - Sources of Energy - P255 - Q10
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
It is not possible to completely reduce the consumption of fossil fuels. However, some measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.
Chap 15 - Our Environment
Chap 15 - Our Environment - P257 - Q1
Why are some substances biodegradable and some non-biodegradable?
substances such as metal, glass, plastic, etc. which cannot be decomposed by the living organisms are non-biodegradable wastes.
substances such as paper, vegetable wastes, etc. that can be easily broken down by enzymes are biodegradable wastes
Chap 15 - Our Environment - P257 - Q2
Give any two ways in which biodegradable substances would affect the environment.
Biodegradable substances affect the environment in the following ways:
(i) The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. T
(ii)These substances after decomposition release that carbon back into the atmosphere.
Chap 15 - Our Environment - P257 - Q3
Give any two ways in which non-biodegradable substances would affect the environment.
Non-biodegradable substances affect the environment in the following ways:
(i) They contaminate soil and water resources as they cannot be decomposed by micro-organisms.
(ii) when accidentally eaten by stray animals, can harm them and can even cause their death.
Chap 15 - Our Environment - P261 - Q1
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
A trophic level is the level of species in an ecosystem on the basis of the source of nutrition such as producers, primary consumers, secondary consumers, etc.
Various trophic levels are connected through food chains. For example, in an aquatic food chain, phytoplanktons are the producers, zooplanktons are the primary consumers, and small fish is the secondary consumer and so on.
Chap 15 - Our Environment - P261 - Q2
What is the role of decomposers in the ecosystem?
Decomposers include micro-organisms such as bacteria and fungi that obtain nutrients by breaking down the remains of dead plants and animals. The body of dead plants and animals into simple inorganic raw materials, such as CO2, H2O, and some nutrients.
Chap 15 - Our Environment - P264 - Q1
What is ozone and how does it affect any ecosystem?
The high energy UV radiations break down O2 molecules into nascent oxygen.
(Nascent Oxygen)
Then, this free oxygen atom combines with an oxygen molecule to form ozone.
In recent years, the amount of ozone in the atmosphere is getting depleted.
This ozone depletion causes a greater amount of ultra violet radiation to enter earth’s atmosphere. This has an indirect effect on the ecosystem.(Ecosystem includes both the biological community and the non-living components of an area). It results in the death of many phytoplanktons, thereby affecting the process of photosynthesis. Plants utilise atmospheric CO2 to make their food. In the absence of plants, the levels of CO2 in the atmosphere will increase, which would in turn lead to an increase in global warming.
Chap 15 - Our Environment - P264 - Q1
Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
(c)Fruit-peels, cake, and lime-juice
(d)Cake, wood, and grass
Chap 15 - Our Environment - P264 - Q2
Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
(b) Grass, goat, and human
Chap 15 - Our Environment - P264 - Q3
Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
(d) All of the above
Chap 15 - Our Environment - P265 - Q4
What will happen if we kill all the organisms in one trophic level?
Various trophic levels are connected through the food chains. If all the organisms of any one trophic level are killed, then it will disrupt the entire food chain.
This is just an example of one food chain. However, in nature, food chains are not isolated. They are interconnected in the form of food web. Therefore, killing all the plants of an area will not only affect the deer, it will also affect other herbivores such as goat, cattle, sheep, etc.
Chap 15 - Our Environment - P265 - Q5
Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Organisms of all trophic levels are equally important and are an integral part of the ecosystem.
Now let us suppose that all the deer (herbivores) are killed in a region. This can lead to an increase in the number of producers. At the same time, there will be an increase in the number of other herbivores such as rabbits, goat, sheep, etc. due to less competition. This will also lead to the increase in population of only consumers of these increased herbivores. Thus, the balance in the ecosystem gets disturbed if any of its component organisms are removed.
Chap 15 - Our Environment - P265 - Q6
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Biomagnification is the increase in the concentration of pollutants or harmful chemicals within each step of the food chain. DDT was sprayed and the producers were found to have 0.04 ppm concentration of DDT. Since many types of planktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as one sea gull eats many clams. Hawk, the top carnivore, has the highest concentration of DDT.
Chap 15 - Our Environment - P265 - Q7
What are the problems caused by the non-biodegradable wastes that we generate?
Non-biodegradable substances affect the environment in the following ways:
(i) Since the non-biodegradable substances cannot be broken down, they get accumulated and thus contaminate the soil and the water resources.
(ii) These substances, when accidentally eaten by some stray animal, can harm them and can even cause their death.
Chap 15 - Our Environment - P265 - Q8
If all the waste we generate is biodegradable, will this have no impact on the environment?
The problem associated with waste management and disposal will also not occur. The population of decomposers will increase to breakdown the extra biodegradable waste generated.
Chap 15 - Our Environment - P265 - Q9
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ozone depletion occurs widely in the stratosphere. However, it is more prominent over the Antarctic region and is known as the ozone hole
* It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
* It can result in the death of many phytoplanktons that leads to increased global warming.
Chap 16 - Management of Natural Resources
Chap 16 - Management of Natural Resources - P269 - Q1
What changes can you make in your habits to become more environment-friendly?
Because objects made of plastic do not get decomposed easily. Besides soil fertility, they badly affect our environment. We should dispose the wastes safely and not disperse in public places. These are a few things that can be done to become more environment- friendly.
Chap 16 - Management of Natural Resources - P269 - Q2
What would be the advantages of exploiting resources with short-term aims?
We should not exploit resources for our short term gains as this would only lead to depletion of natural resources for the present generation as well as generations to come. Hence, we can say that there are hardly any advantages of exploiting natural resources for short term gains.
Chap 16 - Management of Natural Resources - P269 - Q3
How would these advantages differ from the advantages of using a long-term perspective in managing our resources?
Management ensures uniform distribution among the people. It conserves the natural resources for many years and not just for a few years, as in the case of a short-term perspective in conserving natural resources.
Chap 16 - Management of Natural Resources - P269 - Q4
Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources?
Natural resources of the Earth must be distributed among the people uniformly so that each and every one gets his share of the resource.
Human greed, corruption, and the lobby of the rich and powerful are the forces working against an equitable distribution of resources.
Chap 16 - Management of Natural Resources - P273 - Q1
Why should we conserve forests and wildlife?
A large number of tribes are the habitants in and around the forests. If the forests are not conserved, then it may affect these habitants. Without proper management of forest and wildlife, the quality of soil, the water sources, and even the amount of rainfall may be affected. Without forest and wildlife, life would become impossible for human beings.
Chap 16 - Management of Natural Resources - P273 - Q2
Suggest some approaches towards the conservation of forests.
(a) People should show their participation in saving the forest by protesting against the cutting of trees. For example, Chipko Andolan
(b) Planting of trees should be increased. Rate of afforestation must be more than that of deforestation.
(c) Some people cut precious trees such as Chandan to earn money. Government should take legal steps to catch these wood smugglers.
Chap 16 - Management of Natural Resources - P276 - Q1
Find out about the traditional systems of water harvesting/management in your region.
One of the traditional systems of water harvesting used in our region is tanks.
Chap 16 - Management of Natural Resources - P276 - Q2
Compare the above system with the probable systems in hilly/mountainous areas or plains or plateau regions.
In plains, the water harvesting structures are crescent-shaped earthen embankments. These are low, straight, and concrete.
In hilly regions, It involves a collection of rain water in a stream, which is then diverted into man-made channels down the hill sides.
Chap 16 - Management of Natural Resources - P276 - Q3
Find out the source of water in your region/locality. Is water from this source available to all people living in that area?
The source of water in our region is ground water. Water from the source is available to all the people living in that area.
Chap 16 - Management of Natural Resources - P278 - Q1
What changes would you suggest in your home in order to be environment-friendly?
Changes that can be undertaken in our homes to be environment-friendly are listed below:
(i)Throw biodegradable and non-biodegradable waste into separate bins.
(ii)Construct composting pits.
(iii)Food items such as jam, pickles, etc., come packed in plastic bottles. These bottles can later be used for storing things in the kitchen.
Chap 16 - Management of Natural Resources - P278 - Q2
Can you suggest some changes in your school which would make it environment-friendly?
Changes that can be undertaken in our schools to make it environment friendly are listed below:
(i) Turn the taps off when not in use.
(ii) Biodegradable and non-biodegradable wastes should be thrown into separate bins.
Working...
Chap 16 - Management of Natural Resources - P278 - Q3
We saw in this chapter that there are four main stakeholders when it comes to forests and wildlife. Which among these should have the authority to decide the management of forest produce? Why do you think so?
Because the forest department is the care taker of the forest land and is responsible for any damage to the forest.
Chap 16 - Management of Natural Resources - P279 - Q4
How can you as an individual contribute or make a difference to the management of (a) forests and wildlife, (b) water resources and (c) coal and petroleum?
(a) Forest and wildlife:
(i) We should protest against the poaching of wild animals.
(ii) We should stop the annexation of forest land for our use.
(b) Water resources:
(i) We should practice rainwater harvesting.
(ii) We should avoid the discharge of sewage and other wastes into rivers and other water resources.
(c) Coal and petroleum:
(i) We should stop using coal as a fuel (angithis).
(ii)We should use alternative sources of energy such as hydro-energy and solar energy instead of depending largely on coal and petroleum.
Working...
Chap 16 - Management of Natural Resources - P279 - Q5
What can you as an individual do to reduce your consumption of the various natural resources?
Natural resources such as water, forests, coal and petroleum, etc. are important for the survival of human beings. The ways in which we can reduce the consumption of various natural resources are as follows:
(i) We should practice rainwater harvesting.
(ii) We should practice car pooling to avoid the excessive use of petroleum.
(iii) We should use alternative sources of energy such as hydro-energy and solar energy.
Chap 16 - Management of Natural Resources - P279 - Q6
List five things you have done over the last one week to −
(a) conserve our natural resources
(b) increase the pressure on our natural resources
(a) To conserve our natural resources:
(i) Travel by a CNG bus for long distances and walk for short distances.
(ii) Use recycled paper
(iii) Throw biodegradable and non-biodegradable waste into separate bins
(iv) Plant trees
(v) Harvest rainwater
(b) To increase the pressure on our natural resources:
(i) Use non-renewable resources of energy
(ii) Waste water
(iii) Waste electricity
(iv) Use plastics and polythene bags for carrying goods
(v) Use escalators
Chap 16 - Management of Natural Resources - P279 - Q7
On the basis of the issues raised in this chapter, what changes would you incorporate in your life-style in a move towards a sustainable use of our resources?
One should incorporate the following changes in life-style in a move towards a sustainable use of our resources:
(i) Throw biodegradable and non-biodegradable waste into separate bins.
(ii) Waste minimum amount of water while using and repair leaking taps.
(iii) Practice rainwater harvesting.
(iv) Avoid using vehicles for short distances. Instead, one can walk or cycle to cover short distances. To cover long distances, one should take a bus instead of using personal vehicles.
(v) Switch off electrical appliances when not in use.
(vi) Use fluorescent tubes in place of bulbs to save electricity.
(vii) Take stairs and avoid using lifts.
(viii) During winters, wear an extra sweater to avoid using heaters.