Class 10 NCERT Science Questions -

Here all the NCERT Science Questions for Class 10 CBSE Board

Chapter – Chemical Reactions and Equations

Inside

1. Why should a magnesium ribbon be cleaned before burning in air?

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

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.

4. A solution of a substance ‘X’ is used for whitewashing.

(i) Name the substance ‘X’ and write its formula.

(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

5. 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.

6 . Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

7. Give an example of a double displacement reaction other than the one given in Activity 1.10.

8. 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)

Exercise

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.

(d) Lead oxide is getting reduced.

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b) and (c)

(iv) all

2. Fe2O3 + 2Al ® Al2O3 + 2Fe The above reaction is an example of a

(a) combination reaction.

(b) double displacement reaction.

(d) displacement reaction.

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.

(d) Iron salt and water are produced.

4. What is a balanced chemical equation? Why should chemical equations be balanced?

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.

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

6. Balance the following chemical equations.

(a) HNO3 + Ca(OH)2 ® Ca(NO3)2 + H2O

(b) NaOH + H2SO4 ® Na2SO4 + H2O

(d) BaCl2 + H2SO4 ® BaSO4 + HCl

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

(d) Barium chloride + Potassium sulphate ® Barium sulphate + Potassium chloride

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)

(d) Magnesium(s) + Hydrochloric acid(aq) ® Magnesium chloride(aq) + Hydrogen(g)

9. What does one mean by exothermic and endothermic reactions? Give examples.

10. Why is respiration considered an exothermic reaction? Explain.

11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

15. What do you mean by a precipitation reaction? Explain by giving examples.

16. Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation

(b) Reduction

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.

18. Why do we apply paint on iron articles?

19. Oil and fat containing food items are flushed with nitrogen. Why?

20. Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity

Chapter – Acid , Bases and Salts

Inside

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?

1. Why should curd and sour substances not be kept in brass and copper vessels?

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?

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.

4. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

5. Why does an aqueous solution of an acid conduct electricity?

6. Why does dry HCl gas not change the colour of the dry litmus paper?

7. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

8. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?

9. How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?

10. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

11. What effect does the concentration of H+(aq) ions have on the nature of the solution?

12. Do basic solutions also have H+(aq) ions? If yes, then why are these basic?

13. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

14. What is the common name of the compound CaOCl2?

15. Name the substance which on treatment with chlorine yields bleaching powder.

16. Name the sodium compound which is used for softening hard water.

17. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

18. Write an equation to show the reaction between Plaster of Paris and water.

Exercise

1. A solution turns red litmus blue, its pH is likely to be

(a) 1 (b) 4 (c) 5 (d) 10

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

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

4. Which one of the following types of medicines is used for treating indigestion?

(a) Antibiotic

(b) Analgesic

(d) Antiseptic

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.

(d) dilute hydrochloric acid reacts with iron filings.

6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

7. Why does distilled water not conduct electricity, whereas rain water does?

8. Why do acids not show acidic behaviour in the absence of water?

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?

(d) weakly acidic?

(e) weakly alkaline?

Arrange the pH in increasing order of hydrogen-ion concentration.

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. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

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?

13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

14. What is a neutralisation reaction? Give two examples.

15. Give two important uses of washing soda and baking so

Chapter – Metals and Non Metals

Inside

1. 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.

2. Explain the meanings of malleable and ductile.

3. Why is sodium kept immersed in kerosene oil?

4. Write equations for the reactions of

(i) iron with steam

(ii) calcium and potassium with water

5. 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.

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.

6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.

7. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

8. (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?

9. Why do ionic compounds have high melting points?

10. Define the following terms.

(i) Mineral (ii) Ore (iii) Gangue

11. Name two metals which are found in nature in the free state.

12. What chemical process is used for obtaining a metal from its oxide?

13. Which metals do not corrode easily?

14. What are alloys?

Exercise

1. Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl2 solution and aluminium metal

(d) AgNO3 solution and copper metal.

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease

(b) Applying paint

(d) All of the above.

3. 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

(d) iron.

4. 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.

(d) zinc is less reactive than tin.

5. 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.

6. What are amphoteric oxides? Give two examples of amphoteric oxides.

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

8. In the electrolytic refining of a metal M, what would you take as the anode, the

cathode and the electrolyte?

9. 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.

(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.

10. State two ways to prevent the rusting of iron.

11. What type of oxides are formed when non-metals combine with oxygen?

12. Give reasons

(a) Platinum, gold and silver are used to make jewellery.

(b) Sodium, potassium and lithium are stored under oil.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

13. 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.

14. Differentiate between metal and non-metal on the basis of their chemical properties.

15. A man went door to door posing as a goldsmith. He promised to bring back the

glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold

bangles to him which he dipped in a particular solution. The bangles sparkled

like new but their weight was reduced drastically. The lady was upset but after a

futile argument the man beat a hasty retreat. Can you play the detective to find

out the nature of the solution he had used?

16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Chapter – carbon and its compounds

1. What would be the electron dot structure of carbon dioxide which has the formula CO2?

2. 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.)

3. How many structural isomers can you draw for pentane?

4. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

5. What will be the formula and electron dot structure of cyclo pentane?

6. Draw the structures for the following compounds.

(i) Ethanoic acid (ii) Bromo pentane*

(iii) Butanone (iv) Hexanal.

*Are structural isomers possible for bromo pentane?

7. How would you name the following compounds?

(i) CH3—CH2—Br (ii)

(iii)

8. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

9. A mixture of oxygen and ethyne is burnt for welding. Can you tell why

a mixture of ethyne and air is not used?

10. How would you distinguish experimentally between an alcohol and

a carboxylic acid?

11. What are oxidising agents?

12. Would you be able to check if water is hard by using a detergent?

13. 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?

Exercise

1. Ethane, with the molecular formula C2H6 has

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(d) 9 covalent bonds.

2. Butanone is a four-carbon compound with the functional group

(a) carboxylic acid.

(b) aldehyde.

(d) alcohol.

3. 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.

(d) the fuel is burning completely.

4. Explain the nature of the covalent bond using the bond formation in CH3Cl.

5. Draw the electron dot structures for

(a) ethanoic acid.

(b) H2S.

(d) F2 .

6. What is an homologous series? Explain with an example.

7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

9. Why are carbon and its compounds used as fuels for most applications?

10. Explain the formation of scum when hard water is treated with soap.

11. What change will you observe if you test soap with litmus paper (red and blue)?

12. What is hydrogenation? What is its industrial application?

13. Which of the following hydrocarbons undergo addition reactions:

C2H6, C3H8, C3H6, C2H2 and CH4.

14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

15. Explain the mechanism of the cleaning action of soaps.

Light

Define law of Reflection
Write down image formation by plane mirror
Define the term a) pole b) center of curvature c) Radius of Curvature d) principal axis e) Focus f) focal length g ) Aperture
Draw Image formation by Concave Mirror
Draw Image formation by Convex Mirror
Write down the uses of Convex and concave mirror
Draw The New Cartesian Sign Convention for spherical mirrors
Define Magnification of convex and concave mirror
A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located at 5.00 m from this mirror, find the position, nature and size of the image. Ans- 1.15m, 0.23 factor
An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of focal length 15.0 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Find the nature and the size of the image. Ans – 37.5 cm, h ( -6.0 cm) The image is inverted and enlarged.
Draw Refraction of light through a rectangular glass slab
Define law of Refraction of light
Define Refractive Index
Image Formation by convex mirror Using Ray Diagrams
Image Formation by concave mirror Using Ray Diagrams
A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also, find the magnification produced by the lens. Ans – (-30 cm), +0.33
A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification. (V +30 cm) , m = (-2)
Define Power of lens, Write SI unit of Power
Power of concave lens is ——– and power of convex lens is —————-

Exercise Questions

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.
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.
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.
The magnification produced by a plane mirror is +1. What does this mean?
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.
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.
Find the focal length of a lens of power – 2.0 D. What type of lens is this?
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?

Inside questions

Define the principal focus of a concave mirror
The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Name a mirror that can give an erect and enlarged image of an object.
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Find the focal length of a convex mirror whose radius of curvature is 32 cm.
A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?
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?
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.
Find out, from Table 9.3, the medium having highest optical density. Also find the medium with lowest optical density.
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table 9.3
The refractive index of diamond is 2.42. What is the meaning of this statement?
Define 1 dioptre of power of a lens.
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.
Find the power of a concave lens of focal length 2 m

Previous year question

2026

A convex lens of focal length is 15 cm, is forming a real image . if the size of image is same as the size of object, then the position of object and position of image

Chapter – Human Eye

Inside

1. What is meant by power of accommodation of the eye?

2. 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?

3. What is the far point and near point of the human eye with normal vision?

4. 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?

Exercise

1. The human eye can focus on objects at different distances by adjusting the focal

length of the eye lens. This is due to

(a) presbyopia. (b) accommodation.

2. The human eye forms the image of an object at its

(a) cornea. (b) iris. (c) pupil. (d) retina.

3. 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.

4. 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.

5. 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?

6. 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?

7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

8. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

9. What happens to the image distance in the eye when we increase the distance of an object from the eye?

10. Why do stars twinkle?

11. Explain why the planets do not twinkle.

12. Why does the sky appear dark instead of blue to an astronaut?

Chapter – Electricity

Inside

1. What does an electric circuit mean?

2. Define the unit of current.

3. Calculate the number of electrons constituting one coulomb of charge

4. Name a device that helps to maintain a potential difference across a conductor.

5. What is meant by saying that the potential difference between two points is 1 V?

6. How much energy is given to each coulomb of charge passing through a 6 V battery?

7. On what factors does the resistance of a conductor depend?

8. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

9. 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?

9. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

5. Use the data in Table 11.2 to answer the following –

(a) Which among iron and mercury is a better conductor?

(b) Which material is the best conductor?

6. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 W resistor, an 8 W resistor, and a 12 W resistor, and a plug key, all connected in series.

7 . Redraw the circuit of Question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12 W resistor. What would be the readings in the ammeter and the voltmeter?

8. Judge the equivalent resistance when the following are connected in parallel – (a) 1 W and 106 W, (b) 1 W and 103 W, and 106 W.

9. An electric lamp of 100 W, a toaster of resistance 50 W, and a water filter of resistance 500 W 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?

10. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

11. How can three resistors of resistances 2 W, 3 W, and 6 W be connected to give a total resistance of (a) 4 W, (b) 1 W?

12. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 W, 8 W, 12 W, 24 W?

13. Why does the cord of an electric heater not glow while the heating element does?

14. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

15. An electric iron of resistance 20 W takes a current of 5 A. Calculate the heat developed in 30 s.

16. What determines the rate at which energy is delivered by a current?

17. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.

Exercise

1. 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 –

(a) 1/25 (b) 1/5 (c) 5 (d) 25

2. Which of the following terms does not represent electrical power in a circuit?

(a) I2R (b) IR2 (c) VI (d) V2/R

3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –

(a) 100 W (b) 75 W (c) 50 W (d) 25 W

4. 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

5. How is a voltmeter connected in the circuit to measure the potential difference between two points?

6. A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10–8 W m. What will be

the length of this wire to make its resistance 10 W? How much does the resistance change if the diameter is doubled?

7. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –

I (amperes) 0.5 1.0 2.0 3.0 4.0

V (volts) 1.6 3.4 6.7 10.2 13.2

Plot a graph between V and I and calculate the resistance of that resistor.

8. 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.

9. A battery of 9 V is connected in series with resistors of 0.2 W, 0.3 W, 0.4 W , 0.5 W and 12 W, respectively. How much current would flow through the 12 W resistor?

10. How many 176 W resistors (in parallel) are required to carry 5 A on a 220 V line?

11. Show how you would connect three resistors, each of resistance 6 W, so that the combination has a resistance of (i) 9 W, (ii) 4 W.

12. 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?

13. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 W resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

14. Compare the power used in the 2 W resistor in each of the following circuits:

(i) a 6 V battery in series with 1 W and 2 W resistors, and (ii) a 4 V battery in parallel with 12 W and 2 W resistors.

15. 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?

16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

17. An electric heater of resistance 44 Ù draws 5 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.

18. 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?

(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?

Chapter – Magnetic effect of Current

Inside

1. Why does a compass needle get deflected when brought near a bar magnet?

2. Draw magnetic field lines around a bar magnet.

3. List the properties of magnetic field lines.

4. Why don’t two magnetic field lines intersect each other?

5. 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.

6. The magnetic field in a given region is uniform. Draw a diagram to represent it

7. 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.

(d) is the same at all points.

8. 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.)

mass (b) speed (c) velocity (d) momentum

9. In Activity 12.7, 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?

10. 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

11. Name two safety measures commonly used in electric circuits and appliances.

12. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

13. What precaution should be taken to avoid the overloading of domestic electric circuits?

Exercise

1. 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.

(d) The field consists of concentric circles centred on the wire.

2. At the time of short circuit, the current in the circuit

(a) reduces substantially.

(b) does not change.

(d) vary continuously.

3. State whether the following statements are true or false.

(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.

(b) A wire with a green insulation is usually the live wire of an electric supply.

4. List two methods of producing magnetic fields.

5. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

6. 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?

7. 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.

8. When does an electric short circuit occur?

9. What is the function of an earth wire? Why is it necessary to earth metallic

appliances?

Chapter – Life Process

Insider

1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

2. What criteria do we use to decide whether something is alive?

3. What are outside raw materials used for by an organism?

4. What processes would you consider essential for maintaining life?

5. What are the differences between autotrophic nutrition and heterotrophic nutrition?

6. Where do plants get each of the raw materials required for photosynthesis?

7. What is the role of the acid in our stomach?

8. What is the function of digestive enzymes?

9. How is the small intestine designed to absorb digested food?

10. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

11. What are the different ways in which glucose is oxidised to provide energy in various organisms?

12. How is oxygen and carbon dioxide transported in human beings?

13. How are the lungs designed in human beings to maximise the area for exchange of gases?

14. What are the components of the transport system in human beings? What are the functions of these components?

15. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

16. What are the components of the transport system in highly organised plants?

17. How are water and minerals transported in plants?

18. How is food transported in plants?

19. Describe the structure and functioning of nephrons.

20. What are the methods used by plants to get rid of excretory products?

21. How is the amount of urine produced regulated?

Exercise

1. The kidneys in human beings are a part of the system for

(a) nutrition. (c) excretion.

(b) respiration. (d) transportation.

2. The xylem in plants are responsible for

(a) transport of water. (b) transport of food. (c) transport of amino acids.

(d) transport of oxygen.

3. The autotrophic mode of nutrition requires

(a) carbon dioxide and water. (c) sunlight.

(b) chlorophyll. (d) all of the above.

4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in

(a) cytoplasm. (c) chloroplast.

(b) mitochondria. (d) nucleus.

5. How are fats digested in our bodies? Where does this process take place?

6. What is the role of saliva in the digestion of food?

7. What are the necessary conditions for autotrophic nutrition and what are its byproducts?

8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

9. How are the alveoli designed to maximise the exchange of gases?

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

11. Describe double circulation of blood in human beings. Why is it necessary?

12. What are the differences between the transport of materials in xylem and phloem?

13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Chapter – Control and Coordination

Inside

1. What is the difference between a reflex action and walking?

2. What happens at the synapse between two neurons?

3. Which part of the brain maintains posture and equilibrium of the body?

4. How do we detect the smell of an agarbatti (incense stick)?

5. What is the role of the brain in reflex action?

6. What are plant hormones?

7. How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?

8. Give an example of a plant hormone that promotes growth.

9. How do auxins promote the growth of a tendril around a support?

10. Design an experiment to demonstrate hydrotropism

11. How does chemical coordination take place in animals?

12. Why is the use of iodised salt advisable?

13. How does our body respond when adrenaline is secreted into the blood?

14. Why are some patients of diabetes treated by giving injections of insulin?

Exercise

1. Which of the following is a plant hormone?

(a) Insulin

(b) Thyroxin

(d) Cytokinin.

2. The gap between two neurons is called a

(a) dendrite.

(b) synapse.

(d) impulse.

3. The brain is responsible for

(a) thinking.

(b) regulating the heart beat.

(d) all of the above.

4. What is the function of receptors in our body? Think of situations where receptors

do not work properly. What problems are likely to arise?

5. Draw the structure of a neuron and explain its function.

6. How does phototropism occur in plants?

7. Which signals will get disrupted in case of a spinal cord injury?

8. How does chemical coordination occur in plants?

9. What is the need for a system of control and coordination in an organism?

10. How are involuntary actions and reflex actions different from each other?

11. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.

12. What is the difference between the manner in which movement takes place in asensitive plant and the movement in our legs?

Chapter – How do Organism Reproduce

Inside

1. What is the importance of DNA copying in reproduction?

2. Why is variation beneficial to the species but not necessarily for the individual?

3. How does binary fission differ from multiple fission?

4. How will an organism be benefited if it reproduces through spores?

5. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

4. Why is vegetative propagation practised for growing some types of plants?

5. Why is DNA copying an essential part of the process of reproduction?

6. How is the process of pollination different from fertilisation?

7. What is the role of the seminal vesicles and the prostate gland?

8. What are the changes seen in girls at the time of puberty?

9. How does the embryo get nourishment inside the mother’s body?

9. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Exercise

1. Asexual reproduction takes place through budding in

(a) Amoeba.

(b) Yeast.

(d) Leishmania.

2. Which of the following is not a part of the female reproductive system in human

beings?

(a) Ovary

(b) Uterus

(d) Fallopian tube

3. The anther contains

(a) sepals.

(b) ovules.

(d) pollen grains.

4. What are the advantages of sexual reproduction over asexual reproduction?

5. What are the functions performed by the testis in human beings?

6. Why does menstruation occur?

7. Draw a labelled diagram of the longitudinal section of a flower.

8. What are the different methods of contraception?

9. How are the modes for reproduction different in unicellular and multicellular organisms?

10. How does reproduction help in providing stability to populations of species?

11. What could be the reasons for adopting contraceptive methods?

Chapter – Heredity

Inside

1. 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?

2. How does the creation of variations in a species promote survival?

3. How do Mendel’s experiments show that traits may be dominant or

recessive?

4. How do Mendel’s experiments show that traits are inherited independently?

5. 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?

6. How is the sex of the child determined in human beings?

Exercise

1. 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

(d) TtWw

2. 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?

3. Outline a project which aims to find the dominant coat colour in dogs.

4. How is the equal genetic contribution of male and female parents ensured in

the progeny?

Chapter – Our Environment

Inside

1. What are trophic levels? Give an example of a food chain and state the

different trophic levels in it.

2. What is the role of decomposers in the ecosystem?

3. Why are some substances biodegradable and some non-biodegradable?

4. Give any two ways in which biodegradable substances would affect the environment.

5. Give any two ways in which non-biodegradable substances would affect

the environment.

6. What is ozone and how does it affect any ecosystem?

7. How can you help in reducing the problem of waste disposal? Give

any two methods.

Exercise

1. Which of the following groups contain only biodegradable items?

(a) Grass, flowers and leather

(b) Grass, wood and plastic

(d) Cake, wood and grass

2. Which of the following constitute a food-chain?

(a) Grass, wheat and mango

(b) Grass, goat and human

(d) Grass, fish and goat

3. 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

(d) All of the above

5. What will happen if we kill all the organisms in one trophic level?

6. 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?

7. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

8. What are the problems caused by the non-biodegradable wastes that we generate?

8. If all the waste we generate is biodegradable, will this have no impact on the environment?

10. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Chapter – Chemical Reactions and Equations

Chapter – Acid , Bases and Salts

Chapter – Metals and Non Metals

Chapter – carbon and its compounds

Light

Chapter – Human Eye

Chapter – Electricity

Chapter – Magnetic effect of Current

Chapter – Life Process

Chapter – Control and Coordination

Chapter – How do Organism Reproduce

Chapter – Heredity

Chapter – Our Environment

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