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1Class-VII Physics Question Bank

I. Tick (✔✔✔✔✔) the most appropriate answer.1. Heat gives us a

(a) sensation of hotness(b) sensation of coldness(c) sensation of hotness and coldness(d) none of these

2. The property of matter to increase in size on heating is called(a) thermal work (b) thermal energy(c) thermal expansion (d) thermal contraction

3. In which mode of transfer of heat, molecules pass on heat energy toneighbouring molecules without actually moving from their positions?(a) conduction (b) radiation (c) convection (d) none of these

4. The only liquid in which conduction is possible is(a) alcohol (b) water (c) mercury (d) iodine

5. A device in which heat loss due to conduction, convection andradiation is minimised is(a) solar cooker (b) thermos flask(c) thermometer (d) electric heater

6. Shining surfaces are(a) good absorbers of heat(b) good radiators of heat(c) poor absorbers and poor radiators of heat(d) good absorbers and good radiators of heat

7. Heat which can also get transferred is(a) thermal heat (b) mechanical heat(c) radiant heat (d) none of these

8. The fastest method of heat transfer from a hot body to a cold body is(a) radiation (b) convection (c) conduction (d) none of these

9. Friction between two bodies produces(a) motion (b) expansion (c) heat (d) disequilibrium

4 HEAT


10. During daytime air blows(a) from the land to the sea (b) from the sea to the land(c) from one sea to another (d) none of these

Ans. 1. (c) 2. (c) 3. (a) 4. (c) 5. (b) 6. (c)7. (c) 8. (a) 9. (c) 10. (b)

II. Fill in the blank spaces by choosing correct word from the given list.List : rollers, air girders, poor, solids, cubical

1. Convection cannot take place in______________.2. The liquids and gases have only______________ expansion.3. Bridges are mounted on______________ to prevent their collapse.4. Shining bodies are______________ absorbers of radiant heat.5. Radiant heat can easily pass through______________.

Ans. 1. solids 2. cubical 3. rollers4. poor 5. air girders

III. Fill in the blanks.1. Solids ____________ on heating and ____________ on cooling.2. Among matter _________ expands the most and _______ the least.3. Two bodies are said to be in the state of thermal ____________ if

there is no transfer of heat taking place.4. Liquids and gases are generally ____________ conductors of heat.5. Ocean current are caused by the setting up of __________ in water.6. During night time cool breeze blows from _________ to ________.7. ____________ and ____________ are good conductors of heat.8. Transfer of heat takes place from a body at __________ temperature

to a body at ____________ temperature.9. Transfer of heat may take place by either ___________, _________

or ____________.10. Black surfaces are better __________ of heat than polished surfaces.11. Heat is a form of ____________.12. The fixed temperature at which matter is in a liquid state changes to

its solid state is called ____________.13. Temperature is a measure of ____________ of a body.14. Increase in size of the object when heated is called ____________.


15. Thermal expansion is maximum in ____________.16. Temperature is the degree of ____________ of a body.17. Heating of metals is through the mechanism of ____________.18. Heat from the sun reaches us through the mode of ____________.19. Land and sea breezes are caused by ____________ currents.20. Example of a solid that sublimes is ____________.

Ans. 1. expand, contract 2. gas, solid 3. equilibrium4. bad 5. convection 6. land, sea7. gold, silver 8. higher, lower9. conduction, convection, radiation

10. absorber 11. energy 12. freezing point13. hotness or coldness 14. expansion 15. gases16. hotness or coldness 17. conduction 18. radiation19. convection 20. iodine

IV. The statements given below are incorrect. Write the correctstatements.

1. The heat coming from the sun travels by convection.Ans. The heat coming from the sun travels by radiation.

2. More is the heating, less is the expansion of solids.Ans. More is the heating, more is the expansion of solids.

3. Thermal expansion is always a nuisance.Ans. Thermal expansion is not always a nuisance.

4. We can hold a metal rod for a longer time than a glass rod whenboth the rods are heated.

Ans. We can hold a glass rod for a longer time than a metal rod whenboth the rods are heated.

5. Iron is a better conductor of heat than copper.Ans. Copper is a better conductor of heat than iron.

6. Air conducts heat.Ans. Air does not conduct heat.

7. People prefer wearing black clothes in summer.Ans. People prefer wearing white clothes in summer.


8. Solids expand more than liquids and gases.Ans. Solids expand less than liquids and gases.

9. Expansion of liquids is different but of all gases is same.Ans. Expansion of all gases and liquids are different.

10. Mud houses are hot in summer and cold in winter.Ans. Mud houses are cold in summer and hot in winter.

V. Find the odd-one out. Give reasons for your choice.1. Conduction, convection, expansion, radiation

Ans. Expansion. Conduction, convection and radiation, all are the modesof transference of heat while expansion is the property of materials.

2. Wood, paper, silver, plasticAns. Silver. Wood, paper and plastic, all are bad conductor of heat and

electricity while silver is a good conductor of heat and electricity.3. Gold, copper, cork, mercury

Ans. Cork. Gold, copper and mercury all are good conductors of heat andelectricity while cork is bad conductor of heat and electricity.

4. Thermos flask, igloos, candle, ice-boxAns. Candle. Thermos flask, igloos and ice-box all are used to prevent loss

of heat while candle is used for light.5. Kettles, cricket bat, electric press, ovens

Ans. Cricket bat. Kettles, electric press and ovens, all are used by man forheating purpose while cricket bat is used by players to play the cricket.

VI. Match the following.1. good conductor of heat (a) igloos2. bad conductor of heat (b) solar system3. convection current (c) copper4. double-walled houses (d) air5. radiant heat (e) wind current

Ans. 1. (c), 2. (d), 3. (e), 4. (a), 5. (b)


VII. Differentiate between the following.1. Boiling and evaporation

Ans. Boiling Evaporation(i) Boiling takes place trough

the whole mass of theliquid.

(ii) Boiling is a fast process.(iii) Boiling starts only at fixed

temperature.

2. Conduction and convectionAns. Conduction Convection

(i) Conduction is the transfer ofheat from one particle toanother particle without theactual movement of theparticle.

(ii) Transfer of heat byconduction occurs in solids.

3. Conductors of heat and insulators.Ans. Conductors of heat Insulators

(i) The substances throughwhich heat conductssmoothly are calledconductors of heat.

(ii) All metals like gold, silver,copper, etc. conducts heat

(iii) Heat conductors are used tomade kitchen utensils.

VIII. Give reasons for the following.

Evaporation takes place only atthe surface of the liquid.

Evaporation is a slow process.Evaporation takes place at alltemperatures.

Convection is the transfer ofheat by the actual movementof molecules from one part toanother.

Transfer of heat by convectionoccurs in liquids and gases.

The substances which do notconduct heat are called badconductors of heat orinsulators.Wood, paper, plastic, wool,etc. do not conduct heat, sothey are insulators.Insulators are used to madehandle of kettles, teapots etc.


1. We wear woollen clothes in winter.Ans. We use woollen clothes in winter because woollen clothes trap air in

between our body and themselves. The trapped air, therefore, doesnot let the heat of our body escape to the surroundings and we staywarm.

2. Ice is wrapped in saw dust or a woollen blanket.Ans. Melting of ice occurs at room temperature so we have to wrap it in

saw dust or a woollen blanket because they contain large amount oftrapped air which is bad conductor of heat and does not allow theheat from outside to reach the ice.

3. Why do houses with thatched roofs keep cool in summers?Ans. Houses with thatched roofs keep cool in summer, as compared to

houses with concrete roofs. It is because thatched toof contains alarge amount of trapped air which is bad conductor of heat. Henceheat from outside does not flow in thatched roof house. Thus theyremain cool in summer.

4. Why does an ice box have double walls?Ans. Ice-boxes are double-walled containers. There is air in the space

between the two walls. Air being a poor conductor does not let theoutside heat enter the box. The ice in the box, therefore, does notmelt quickly.

5. Cooking pots are provided with wooden or plastic handles. Why?Ans. Cooking pots are provided with wooden or plastic handles because

wood or plastic handles are bad conductors of heat. Hence, theheat from hot appliances does not flow to our hands with the resultthat we can handle them without any difficulty.

6. We prefer white clothes in summer and dark-coloured clothes inwinter. Why?

Ans. People prefer to wear white clothes in summer because of its poorheat absorbing power. They reflect most of heat of the sun fallingon them and absorb very little. On the other hand, dark colouredclothes are good absorber of heat and hence keep our body warmin winter.


7. The top of a roof made of asbestos is painted white.Ans. White colour is poor absorber and good reflector of heat. So that

most of the sunlight fall on the roof is reflected back and the housebecomes cool.

8. Gaps are left in between rails while laying a railway tracks.Ans. Gaps are left in between rails. This is done to provide room for the

rails to expand when the temperature rises. If it is not done, the railswould expand and band on getting heated.

9. Telephone wires are kept slightly loose when they are laid in summer.Ans. We know that every matter expand on heating and contract on

cooling. When telephone wires are fixed, they are left a little loosein summer. This is done to prevent their snapping when they contractin winter.

10. Bridges are mounted on rollers.Ans. Bridges are mounted on the rollers so that they can freely expand

in summer and contract in winter. Therefore, to avoid any damageto the bridge rollers are employed.

11. A thick glass tumbler crack when hot water is poured in it.Ans. We know that substances expand on heating. When we pour hot

water in a glass tumbler, heat is transferred from hot water to glasstumbler then there is unequal expansion of inner and outer surfaceof glass. Due to this uneven expansion a strain builds up in theglass. It is this strain which cracks the glass.

12. The diameter of an iron tyre is kept slightly smaller than the woodenwheel on which this tyre is to be mounted.

Ans. The diameter of an iron tyre is kept slightly smaller than the woodenwheels. Because on heating, it expands and fit over the woodenwheels.

13. We wear a number of garments in winter rather than one thick garment.Ans. A number of garments form many layers of air and air is bad

conductor of heat which prevent the flow of heat from the body tothe surroundings. So, we should wear a number of garments inwinter rather than one thick garment.


14. Heat from the sun heats up earth, but the air in the atmosphere doesnot get heated up.

Ans. Heat is transferred from the sun to earth without heating the air inbetween. This process of transfer of heat is called radiation wherethe medium in which the heat travels does not play any role.

15. Water should not used to put off electrical fires.Ans. Convection is the mode of heat transfer in liquids, taking place by

the actual movement of molecules. So, we should not use water toput off electrical fires. Impure water is a conductor of electricity.

IX. Answer these questions.1. List three effects of heat on an object.

Ans. When we heat an object then it has following effects:(i) It becomes hot, it means, there is rise in temperature.

(ii) It expand in size.(iii) It changes its state such as water boils to form water vapour.

2. Name the three modes of transmissions of heat energy.Ans. Heat can be transferred in the following ways:

(i) Conduction (ii) Convection (iii) Radiation3. Name four good conductors and four bad conductors of heat.

Ans. Copper, silver, gold and iron are good conductors of heat.Wood, paper, cork and plastic are bad conductors of heat.

4. Give three practical uses of good conductors.Ans. Practical uses of good conductors:

(i) Cooking vessels are made of metals so that they can readilyabsorb heat energy and transfer it to food.

(ii) Mercury is used in thermometer because it is good conductorof heat.

(iii) Cooling coils of air-conditioners and refrigerators are made ofcopper as they readily conduct away heat.

5. What is a thermometer?Ans. Thermometer is a device which is used to measure the temperature

of a body or environment. Thermometer is made of a glass tubehaving a fine bore. There is a glass tube bulb at one end of the tube


and other end is open. The bulb is filled with mercury and open endof the tube is sealed. The upper and lower fixed points are markedon the thermometer and the distance between these marks is dividedinto 100 equal parts.

6. Give four reasons for using mercury in a thermometer.Ans. Mercury is used as a thermometric liquid because of the following

reasons:(i) It has a lower freezing point (–39 °C) and a high boiling point

(35 °C). Hence it can be used over a wide range of temperature.(ii) It is shiny liquid metal, hence can be easily seen through the

glass of the thermometer tube.(iii) It has a fairly large expansion for a small change in temperature.(iv) It does not stick to the glass tube.

7. What are standard points?Ans. On the celsius thermometer, the lowest marking is 0 °C and highest

marking is 100 °C. 0 °C corresponds to the temperature of meltingof ice and 100 °C corresponds to the boiling temperature of purewater. These temperatures are called standard points or fixed pointsof a thermometer.

8. What is bimetallic strip?Ans. Plates of two different metals which are riveted together at a number

of points in such a way that they cannot slide on being heateed orcooled, form a bimetallic strip. It is used in refrigerators, automaticelectric iron etc.

9. Give one example of each mode of transference of heat.Ans. (i) Conduction. It is the process of transfer of heat in solids from

one particle to another without the actual movements of the particle.For example, transfer of heat from one end to another end in an ironor copper rods.(ii) Convection. It is the mode of heat transfer in liquid and gasestaking place by the actual movement of molecules from one part toanother. For example, chimneys are fitted in the industries to removeundesirable fumes. The smoke, fumes, hot gases are less dense


than air, therefore, they rise up through the chimneys.(iii) Radiation. It is the transfer of heat from a hot body to a coldbody directly without heating the space between the two bodies.For example, the sun’s heat reaches us across millions miles ofspace. The heat travels by radiations.

10. What do you understand by the terms (a) good conductors (b) badconductors?

Ans. (a) Good conductors: Those substances which allow the heat andelectricity to flow through them easily are called good conductorse.g., copper , aluminium, gold, etc.(b) Bad conductors: Those substances which do not allow theheat and electricity to flow through them are called bad conductorse.g., glass, mica, wool etc.

11. Describe an experiment to prove that water is a bad conductor ofheat.

Ans. Water is a bad conductor of heat. We can prove it by the followingexperiment:Take a test tube, half-filledwith water. Take a ice cubewrapped in copper wiregauze to make it heavy.Drop it into the test tube.Hold the test tube in aninclined position and heatit on the upper level ofwater. We will see that the water at top starts boiling but the ice doesnot melt. This experiment proves that water is a bad conductors ofheat because heat does not travel throughout the water.

12. How will you prove experimentally that amongst the copper andiron rods of same dimensions, copper is a better conductor of heatas compared to iron?


Ans. Take two rods of copperand iron of equal thickness.Dip them in wax. Insert eachof these rods in vessel as infigure. Now pour hot oil inthe vessel. We will find thatas heat travels through therods, wax coating on therods melt. We observe thatwax coating on copper rodhas more melting extent than iron. It proves that conductivity ofcopper is more than iron.

13. Describe an experiment to prove that gases expand on heating.Ans. Gases expand on heating. We can

prove it by a simple experiment:Take a test tube, fit a cork stopperthrough which passes a narrowglass tube. Insert a mercury pelletin the narrow glass tube.On heating the empty glass tubehaving air there, we find that themercury pellet in the glass tube risesindicating the expansion of air in thetest tube.

14. What is thermal expansion?Ans. Substances expand on heating. We know, all matter are made of

molecules. On heating, these molecules vibrate with increased energy.These molecules require more space to vibrate and so the objectexpands. We call this property of expansion of matter on heating asthermal expansion.

15. What is the difference between heat and temperature?Ans. Temperature is a physical quantity that is related to the average kinetic

energy of the molecules of a substance.Heat is a measure of a total energy of a substance i.e., total energyof all molecules put together.

Conductivity of copper is more than iron.

Gases expand on heating


16. Describe an experiment to prove that solids expand on heating.Ans. Take an iron wire and a curtain ring. Slip the curtain ring through the

wire and stretch it between the two stands. Adjust the position ofstands in such a way that wire is just taut that is straight.Now heat the wire by using a burner and observe what happens. Weobserve, the wire no longer remains taut. It proves that solids showthermal expansion.

Thermal expansion in solids

17. What do you understand by the term (a) radiation and (b) radiantheat?

Ans. The heat energy comes from the sun over a large distance betweenthe sun and the earth. There is the third mode of transference of heatenergy where the intervening medium does not play any part. Thismode of transference of heat is called radiations and the heat energytransmitted by the process of radiations is called radiant heat.

18. Why is radiator of motor car painted black?Ans. Black colour is good absorber of heat and also good radiators of

radiant heat. Radiators of motor car painted black because it absorbheat energy from the engine and also radiate it quickly and cool offthe engine.

19. Water is a bad conductor of heat but we heat water without anydifficulty. How is it possible?

Ans. Water is a bad conductor of heat but we heat it without any difficultyby process of heat transfer called convection.Convection is the mode of heat transfer in liquids and gases takingplace by the actual movement of molecules from one part to another.


20. Describe the following terms:(i) sublimation (ii) fusion (iii) melting point

(iv) solidification (v) vapourisation (vi) boiling point(vii) evaporation (viii) condensation

Ans. (i) Sublimation: It is the process due to which a solid directlychanges into gaseous state on heating, and gaseous state so formeddirectly changes into solid state on cooling without changing intoliquid state.(ii) Fusion: It is also called melting. The process due to which asolid changes into liquid state by absorbing heat energy is calledfusion.(iii) Melting point: It is the temperature at which a solid changesinto liquid state is called melting point. For example, melting pointof ice is 0 °C.(iv) Solidification: It is also called freezing. The process due whicha liquid changes into solid state by losing heat energy is calledsolidification.(v) Vapourisation: The process due which a liquid changes intogases state by gaining heat energy is called vapourisation.(vi) Boiling point: It is the temperature at which a liquid changesinto gases state is called boiling point. The boiling point of water is100°C.(vii) Evaporation: The process due to which a liquid changes intogaseous state below its boiling point is called evaporation.(viii) Condensation: It is also called liquefication. The processdue to which a gas changes into liquid state by losing heat energy iscalled condensation.

21. What do you understand by the term ventilation?Ans. Ventilation is the process by which impure and warm air in a room is

continuously replaced by fresh and cool air.The air are heated up by convection currents and moved out fromroom. This air is continuously replaced by fresh air.

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