Transfer of Thermal Energy

Chapter 14 MCQs

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1

A metal spoon and a wooden spoon are placed in hot water. After a short time, the handle of the metal spoon feels hotter.

Which explanation is correct?

A metal particles move from the hot end to the cold end
B free electrons transfer energy through the metal
C wood has more free electrons than metal
D thermal energy cannot travel through wood at all

2

In a metal rod, thermal energy is transferred mainly by:

A convection currents only
B free electrons and vibrating ions
C evaporation from the surface
D compression of air particles inside the metal

3

A metal rod is heated at one end. The other end becomes hot.

Which statement best explains conduction in the rod?

A hot atoms travel along the rod carrying energy
B particles at the hot end vibrate more and transfer energy to neighbouring particles
C cold particles move to the hot end and become warm
D thermal radiation travels only inside the rod

4

Which material is usually the best thermal conductor?

A copper
B glass
C plastic
D wood

5

Which material is usually the best thermal insulator?

A aluminium
B copper
C iron
D trapped air

6

A student holds one end of four rods of equal length and diameter. The other end of each rod is placed in boiling water.

Which rod becomes too hot to hold first?

A copper
B glass
C plastic
D wood

7

A saucepan has a metal base and a plastic handle.

Which row explains this design?

	metal base	plastic handle
A	poor conductor	good conductor
B	good conductor	poor conductor
C	good insulator	good conductor
D	poor conductor	poor conductor

8

A thick carpet helps keep a room warm mainly because:

A carpet is shiny and reflects all infrared
B carpet traps air, and air is a poor conductor
C carpet increases convection in the floor
D carpet absorbs cold from the floor

9

Double-glazed windows reduce thermal energy loss mainly because the air gap:

A is a good conductor
B reduces conduction and convection
C increases radiation from the room
D creates extra cold energy

10

Why is the air gap in double glazing usually narrow?

A to allow strong convection currents
B to reduce convection currents in the trapped air
C to make the glass expand more
D to increase conduction through the air

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11

A vacuum flask has a vacuum between its walls.

Which method or methods of thermal transfer are reduced most directly by the vacuum?

A conduction and convection
B convection and radiation
C radiation only
D conduction only through the glass

12

A vacuum flask has silvered inner surfaces.

What is the main purpose of the silvered surfaces?

A reduce conduction through the vacuum
B reduce convection inside the liquid
C reduce infrared radiation transfer
D increase evaporation from the liquid

13

A vacuum flask has a plastic stopper.

Which thermal transfer is mainly reduced by the stopper?

A conduction and convection through the opening
B radiation through the vacuum only
C convection through the silvered surface
D conduction through empty space

14

A hot drink cools faster when the cup is left uncovered.

Which extra energy transfer process is mainly increased by removing the lid?

A evaporation
B nuclear radiation
C condensation
D melting

15

A student wraps a hot beaker in shiny aluminium foil.

Which energy transfer is most reduced by the shiny outer surface?

A conduction through the glass
B convection inside the liquid
C infrared radiation from the surface
D evaporation from the water surface only

16

Four identical cans contain equal volumes of hot water. Their outer surfaces are different.

Which can loses thermal energy fastest by radiation?

A dull black
B shiny black
C dull white
D shiny silver

17

Four identical cans contain equal volumes of hot water. Their outer surfaces are different.

Which can loses thermal energy slowest by radiation?

A dull black
B dull white
C shiny black
D shiny silver

18

A dull black surface is compared with a shiny silver surface at the same temperature.

Which statement is correct?

A dull black is a good emitter and good absorber of infrared
B dull black is a poor emitter and poor absorber of infrared
C shiny silver is a good emitter and poor absorber of infrared
D shiny silver is a good absorber and poor reflector of infrared

19

A Leslie cube has four different surfaces. Hot water is placed inside it. An infrared detector is placed the same distance from each surface.

Which surface gives the greatest detector reading?

A dull black
B shiny silver
C polished white
D shiny metal

20

A shiny silver surface is useful in a vacuum flask because it is:

A a good emitter and good absorber
B a poor emitter and good reflector
C a good conductor and good emitter
D a poor reflector and good absorber

21

Thermal radiation can travel:

A only through solids
B only through liquids and gases
C through a vacuum
D only by movement of particles

22

Energy from the Sun reaches Earth mainly by:

A conduction through space
B convection through space
C infrared and other electromagnetic radiation
D evaporation of particles from the Sun to Earth

23

Why can thermal radiation travel through a vacuum?

A it is transferred by electromagnetic waves
B it is carried by air molecules
C it is carried by convection currents
D it requires vibrating particles

24

A black car and a white car are parked in sunlight for the same time.

Which car becomes hotter and why?

A black car, because black surfaces are better absorbers of radiation
B white car, because white surfaces are better absorbers of radiation
C black car, because black surfaces are poor absorbers of radiation
D both equally, because colour affects only visible light, not thermal transfer

25

A person wearing dark clothing feels warmer in sunlight than a person wearing light clothing mainly because dark clothing:

A reflects more infrared
B absorbs more radiation
C conducts heat faster
D prevents all evaporation

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26

A beaker of water is heated from below.

What happens to the water at the bottom first?

A it becomes denser and sinks
B it becomes less dense and rises
C it becomes solid and rises
D it becomes less dense and remains fixed

27

Convection occurs in liquids and gases because:

A hot fluid becomes less dense and rises
B hot fluid becomes more dense and sinks
C particles are fixed in a regular lattice
D fluids cannot expand when heated

28

Why does convection not occur in solids?

A solid particles are fixed in position and cannot flow as a bulk fluid
B solids have no particles
C solids cannot conduct thermal energy
D solids have zero density

29

A heater is placed near the ceiling of a room.

Why is this less effective for heating the whole room than placing it near the floor?

A hot air sinks immediately
B warm air remains near the ceiling, reducing convection around the whole room
C cold air rises and stays at the ceiling
D radiation cannot travel downwards

30

A refrigerator has its cooling unit near the top.

Which explanation is correct?

A cooled air becomes denser and sinks, setting up convection
B cooled air becomes less dense and rises
C warm air cannot move inside a refrigerator
D cooling units work only by radiation

31

Sea breezes occur during the day because:

A land heats faster than sea, so air above land rises
B sea heats faster than land, so air above sea rises
C land cools faster than sea, so air above land sinks
D air cannot move above water

32

At night, a land breeze may occur because:

A land stays warmer than sea all night
B sea cools faster than land
C land cools faster than sea, so air above sea rises
D convection stops completely at night

33

A chimney removes smoke from a fireplace mainly because:

A smoke particles are magnetic
B hot gases are less dense and rise
C cold gases rise faster than hot gases
D pressure is always greater at the top of the chimney

34

A student heats water in a flask from the top. Ice is held at the bottom of the flask.

The water near the top can boil while the ice remains unmelted for some time.

What does this show?

A water is a poor conductor
B water is a good conductor
C convection carries heat downwards strongly
D radiation cannot travel through water

35

A student heats water at the bottom of a beaker. The whole beaker of water warms.

Which process mainly transfers energy through the water?

A conduction only
B convection
C radiation only
D evaporation only

36

A lava lamp works because warmed liquid becomes less dense and rises.

Which process is this most similar to?

A conduction in metal
B convection in a fluid
C radiation through vacuum
D condensation on glass

37

A room is heated by a radiator placed near the floor. Warm air rises above the radiator.

What happens next in the convection current?

A cooler air moves down and towards the radiator
B cooler air remains permanently at the ceiling
C warm air becomes denser and falls immediately
D air particles stop moving

38

A convection current forms in a fluid because heating causes:

A an increase in density of the heated fluid
B a decrease in density of the heated fluid
C no change in density
D the fluid to become a solid

39

A student observes dust particles above a hot radiator moving upwards.

Which explanation is best?

A dust is attracted by the metal radiator
B warm air rising carries the dust upwards
C infrared radiation pushes dust upwards directly
D dust particles become massless

40

Which process requires bulk movement of matter?

A conduction in a metal
B convection in air
C radiation from the Sun
D reflection of infrared

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41

A copper rod and an iron rod have the same length and diameter. One end of each rod is heated equally.

The far end of the copper rod warms first.

What conclusion is valid?

A copper has a lower density than iron
B copper is a better thermal conductor than iron
C copper has a lower melting point than iron
D iron cannot conduct thermal energy

42

A student compares heat loss from two identical hot cans.

Can X is dull black.
Can Y is shiny silver.

Both are placed in still air.

Which statement is correct?

A X loses more energy by radiation than Y
B Y loses more energy by radiation than X
C both lose equal energy by radiation because they have equal temperature
D radiation does not occur in air

43

Two identical metal plates are placed in front of an infrared heater.

Plate X is dull black.
Plate Y is shiny silver.

Which plate warms faster and why?

A X, because it absorbs infrared better
B X, because it reflects infrared better
C Y, because it absorbs infrared better
D Y, because shiny surfaces are good emitters

44

A hot object loses energy by radiation at a faster rate when:

A its surface area is smaller
B its temperature is higher
C its surface is shiny silver
D it is placed in a vacuum and radiation is impossible

45

A hot object is placed in a vacuum with no contact with other objects.

How can it lose thermal energy?

A conduction only
B convection only
C radiation only
D conduction and convection only

46

An object is covered with a layer of foam.

Which explanation best describes how foam reduces thermal energy transfer?

A foam contains trapped air, which reduces conduction and convection
B foam is a good metal conductor
C foam increases density of the object
D foam increases evaporation from the object

47

A house loses thermal energy through the roof. Insulating material is placed in the roof space.

Why does this reduce energy loss?

A it traps air and reduces conduction and convection
B it increases convection currents in the roof
C it makes the roof a perfect conductor
D it changes all thermal energy into light

48

A hot water tank is covered with insulating foam and shiny foil.

Which row best describes their purposes?

	foam	shiny foil
A	reduces conduction/convection	reduces radiation
B	reduces radiation only	increases conduction
C	increases convection	reduces conduction through metal
D	increases radiation	reduces convection only

49

A student says, “Conduction, convection and radiation all need particles.”

Which correction is best?

A only radiation needs particles
B conduction and convection need particles, but radiation can travel through a vacuum
C convection and radiation need particles, but conduction does not
D none of them need particles

50

A hot cup of tea cools in a room.

Which row correctly gives examples of energy transfer from the cup?

	conduction	convection	radiation
A	through cup to table	warm air rising from cup	infrared emitted by cup
B	infrared through cup	particles boiling	air becoming solid
C	warm air rising	through vacuum only	silver surface absorbing
D	evaporation through table	conduction by sunlight	convection through vacuum

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Chapter 14 Answer Key

Q	Ans	Q	Ans	Q	Ans	Q	Ans	Q	Ans
1	B	11	A	21	C	31	A	41	B
2	B	12	C	22	C	32	C	42	A
3	B	13	A	23	A	33	B	43	A
4	A	14	A	24	A	34	A	44	B
5	D	15	C	25	B	35	B	45	C
6	A	16	A	26	B	36	B	46	A
7	B	17	D	27	A	37	A	47	A
8	B	18	A	28	A	38	B	48	A
9	B	19	A	29	B	39	B	49	B
10	B	20	B	30	A	40	B	50	A

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Detailed Explanations

1. B

Metals are good thermal conductors mainly because they contain free electrons.
These free electrons move through the metal and transfer energy quickly.
Wood has no free electrons like metals, so it is a poor conductor.
Metal particles do not physically travel from hot end to cold end.

2. B

In metals, thermal energy is transferred by:
- free electrons moving through the metal
- vibrating ions passing energy to neighbouring ions
Convection cannot happen inside a solid metal because the metal does not flow as a fluid.

3. B

At the hot end, particles vibrate more.
They transfer energy to neighbouring particles by collisions/interactions.
In metals, free electrons also help transfer energy quickly.
Hot atoms do not travel along the rod as a whole.

4. A

Copper is one of the best common thermal conductors.
It is often used in saucepan bases and electrical wiring.
Glass, plastic and wood are much poorer thermal conductors.

5. D

Trapped air is a very good thermal insulator.
It reduces conduction because air is a poor conductor.
It reduces convection if trapped in small pockets.
This is why foam, wool, carpets and roof insulation work.

6. A

Copper conducts thermal energy fastest among the listed materials.
So the end being held becomes hot first.
Wood and plastic are poor conductors.
Glass is also a poor conductor compared with copper.

7. B

Metal base:
- good conductor
- transfers energy quickly from flame/hob to food
Plastic handle:
- poor conductor
- reduces energy transfer to the hand
This is a classic application of conductor + insulator design.

8. B

Carpets trap air between fibres.
Trapped air is a poor conductor.
Since the air is trapped, convection is also reduced.
Carpets do not “absorb cold”; cold is not a substance. Classic fake explanation.

9. B

Double glazing has trapped air between two glass panes.
Air is a poor conductor.
If the gap is narrow, convection currents are reduced.
So the air gap reduces conduction and convection.

10. B

If the air gap is too wide, convection currents can form inside it.
A narrow gap traps the air and reduces convection.
This makes double glazing more effective.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. A

A vacuum has no particles.
Conduction needs particles.
Convection needs bulk movement of particles.
Therefore a vacuum reduces conduction and convection.
Radiation can still travel through a vacuum.

12. C

Silvered surfaces are shiny.
Shiny surfaces are poor emitters and poor absorbers of infrared radiation.
They reflect infrared radiation back.
So silvered surfaces reduce thermal energy transfer by radiation.

13. A

The stopper closes the opening.
It reduces:
- conduction through the top
- convection currents carrying warm air/vapour away
- evaporation from the liquid surface
The main answer here is conduction and convection through the opening.

14. A

A lid reduces evaporation.
Removing the lid allows more water molecules to escape.
Evaporation removes energy from the drink.
So the drink cools faster.

15. C

Shiny aluminium foil is a poor emitter and good reflector of infrared radiation.
It reduces energy loss by radiation.
It does not significantly stop conduction through the glass itself.

16. A

Dull black surfaces are the best emitters of infrared radiation.
So a dull black can loses thermal energy fastest by radiation.
Shiny silver would be the slowest.

17. D

Shiny silver surfaces are poor emitters of infrared radiation.
Therefore they lose thermal energy slowest by radiation.
Dull black loses fastest.

18. A

Dull black surfaces are:
- good absorbers of infrared
- good emitters of infrared
Shiny silver surfaces are:
- poor absorbers
- poor emitters
- good reflectors

19. A

Leslie cube compares infrared emission from different surfaces.
Dull black is the best emitter.
Therefore the infrared detector gives the greatest reading for the dull black surface.

20. B

Shiny silver is useful in a vacuum flask because it:
- reflects infrared radiation
- is a poor emitter
- is a poor absorber
This reduces radiation transfer between the flask walls.

21. C

Thermal radiation is electromagnetic radiation.
It does not need particles.
It can travel through a vacuum.
This is why energy from the Sun reaches Earth.

22. C

Space is mostly vacuum.
Conduction and convection cannot transfer energy through vacuum.
Energy from the Sun reaches Earth by electromagnetic radiation, including infrared, visible light and ultraviolet.

23. A

Thermal radiation is transferred by electromagnetic waves.
Electromagnetic waves can travel through a vacuum.
No particles are needed.

24. A

Black surfaces absorb radiation better than white or shiny surfaces.
The black car absorbs more energy from sunlight.
It becomes hotter than the white car.

25. B

Dark clothing absorbs more radiation.
Light clothing reflects more radiation.
Therefore dark clothing feels warmer in sunlight.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. B

Water at the bottom is heated first.
It expands and becomes less dense.
Less dense warm water rises.
Cooler, denser water sinks to replace it.
This forms a convection current.

27. A

Convection happens in fluids: liquids and gases.
Heating makes part of the fluid expand.
Its density decreases.
The less dense fluid rises and cooler denser fluid sinks.

28. A

Solids cannot undergo convection because their particles are fixed in position.
They cannot flow as a bulk fluid.
Solids can transfer energy by conduction, not convection.

29. B

A heater near the ceiling warms air already high in the room.
Warm air stays near the ceiling because it is less dense.
This reduces circulation through the whole room.
A heater near the floor sets up better convection currents.

30. A

A refrigerator cooling unit is near the top.
Air near the cooling unit cools, becomes denser and sinks.
Warmer air rises to replace it.
This sets up convection currents inside the refrigerator.

31. A

During the day, land heats up faster than sea.
Air above land warms, expands and rises.
Cooler air from over the sea moves towards land.
This produces a sea breeze.

32. C

At night, land cools faster than sea.
Sea remains relatively warmer.
Air above the sea rises.
Cooler air moves from land towards sea.
This produces a land breeze.

33. B

Hot gases from a fire are less dense than surrounding cooler air.
They rise up the chimney.
This movement helps remove smoke and draws fresh air into the fireplace.

34. A

Heating from the top does not set up convection through the whole water.
Water is a poor conductor, so little energy reaches the ice at the bottom.
The top can boil while the ice remains for some time.
This shows water is a poor conductor.

35. B

When water is heated from below, convection currents form.
Warm water rises and cooler water sinks.
This transfers energy throughout the water.

36. B

A lava lamp works by convection.
Warmed liquid becomes less dense and rises.
Cooler liquid becomes denser and sinks.

37. A

Warm air rises above the radiator.
Cooler air moves down and towards the radiator.
This completes the convection current.
The room warms by circulating air.

38. B

Heating a fluid causes expansion.
Expansion reduces density.
The less dense fluid rises.
This starts convection.

39. B

Dust particles above a radiator are carried upwards by warm rising air.
The dust is not pushed upwards directly by infrared radiation.
The radiator sets up a convection current.

40. B

Convection requires bulk movement of matter.
In air, warm air rises and cool air sinks.
Radiation does not require matter.
Conduction in solids transfers energy without bulk movement of the material.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. B

The copper rod warms at the far end first.
This shows copper transfers thermal energy faster than iron.
Therefore copper is the better thermal conductor.
It does not prove anything about density or melting point.

42. A

Dull black surfaces are better emitters of infrared radiation than shiny silver surfaces.
So can X loses more energy by radiation than can Y.
Equal temperature does not mean equal radiation loss if surfaces differ.

43. A

Dull black surfaces are better absorbers of infrared radiation.
Plate X absorbs more energy from the infrared heater.
Therefore it warms faster.

44. B

A hotter object emits radiation at a greater rate.
Higher temperature difference with surroundings also increases net energy loss.
Shiny silver surfaces reduce radiation loss, not increase it.

45. C

In a vacuum:
- no conduction through air
- no convection through air
The object can still lose energy by infrared radiation.
Radiation does not require particles.

46. A

Foam contains trapped air pockets.
Trapped air reduces conduction.
Since the air cannot circulate easily, convection is also reduced.
This is why foam is a good insulator.

47. A

Roof insulation traps air.
This reduces conduction and convection.
It slows thermal energy loss through the roof.

48. A

Foam:
- traps air
- reduces conduction and convection
Shiny foil:
- reflects infrared radiation
- reduces radiation transfer
Together they reduce several methods of thermal energy transfer.

49. B

Conduction needs particles.
Convection needs particles and bulk movement of a fluid.
Radiation does not need particles and can travel through a vacuum.
So the student’s statement is wrong.

50. A

Conduction:
- energy transfers through the cup to the table
Convection:
- warm air rises from the cup
Radiation:
- infrared is emitted by the cup
This option correctly matches all three.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Common Traps From This Chapter

Trap	Correct Rule
Metals conduct well	free electrons + vibrating ions
Non-metals conduct poorly	no free electrons
Conduction	particle-to-particle energy transfer
Convection	bulk movement of fluid
Radiation	electromagnetic waves
Radiation through vacuum	possible
Conduction/convection through vacuum	not possible
Hot fluid	expands, becomes less dense, rises
Cold fluid	denser, sinks
Convection in solids	does not occur
Radiator near floor	better convection circulation
Refrigerator cooling unit	placed near top so cold air sinks
Dull black	best absorber and emitter
Shiny silver	poor absorber/emitter, good reflector
Vacuum flask vacuum	reduces conduction and convection
Vacuum flask silvering	reduces radiation
Plastic stopper	reduces conduction, convection and evaporation
Double glazing	trapped air reduces conduction/convection
Narrow air gaps	reduce convection currents
Foam/wool/carpet	trapped air insulation
Sun to Earth	radiation, not conduction/convection
Lid on hot drink	reduces evaporation and convection

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