IGCSE Physics Consequences of Thermal Energy Transfer Questions and Worked Solutions (2.3.4) | 0625

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IGCSE Physics 0625 · Topic 2.3.4

IGCSE Physics Consequences of Thermal Energy Transfer Questions and Worked Solutions

50 topic-wise practice questions on Consequences of Thermal Energy Transfer (Unit 2: Thermal Physics), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.

50 questions24 Core16 Extended10 Challenge129 marksTextbook §2.3 · pp. 115–126
Questions tagged Core are for all candidates (Papers 1 & 3). Questions tagged Extended are Supplement content (Papers 2 & 4). Questions 41–50 are harder Challenge questions. Try each question first, then tap Show solution to check your working.

Topic guide: Consequences of Thermal Energy Transfer

Real situations usually involve several methods of thermal energy transfer at once. This subtopic applies conduction, convection and radiation to cooking, heating, insulation and cooling systems.

Key formulas

No equations to learn in this subtopic — identify the method of transfer in each part of a system.

Prerequisite knowledge

  • Conduction (2.3.1)
  • Convection (2.3.2)
  • Radiation (2.3.3)

Exam tips & common mistakes

  • Name the method AND explain how a feature reduces it
  • Trapped air reduces both conduction and convection
  • Large surface area increases transfer by convection and radiation

Key facts from the syllabus (2.3.4)

  • Heating a pan: conduction through the base, convection in the liquid
  • Room heaters ('radiators') heat mainly by convection
  • Extended a wood or coal fire heats by radiation (to objects in front) and convection (hot gases rise), with conduction through the hearth
  • Extended car radiators — conduction into the fins, convection to the air, some radiation; fins give a large surface area
  • Extended vacuum flask — vacuum stops conduction and convection, silvered walls reduce radiation, stopper reduces convection and evaporation
  • Insulation (loft, cavity wall, double glazing, curtains) traps air to reduce conduction and convection

Textbook: §2.3 Transfer of thermal energy, pp. 115–126

1
Core[3 marks]

Explain how food in a metal pan on a hotplate is heated.

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Method: Conduction through the base; convection in liquid.

Energy is conducted through the metal base, then convection currents carry energy through the liquid food
2
Core[3 marks]

Explain how a convector heater warms a whole room.

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Method: Convection current.

Air near the heater warms, expands, becomes less dense and rises; cooler air sinks to the heater, setting up a convection current
3
Core[2 marks]

Explain why a pan lid speeds up cooking.

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Method: Reduces convection and evaporation losses.

It reduces energy loss by convection and evaporation from the surface
4
Core[2 marks]

Explain why the handle of a pan is made from plastic.

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Method: Insulator.

Plastic is a poor conductor, so the handle stays cool to touch
5
Core[2 marks]

Explain why a hot drink in a cup with a lid cools more slowly.

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Method: Reduces convection/evaporation.

The lid stops warm air rising away and reduces evaporation
6
Core[2 marks]

Explain why a radiator is placed under a window.

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Method: Warms cold air at window.

It heats the cold air near the window, setting up convection currents that circulate warm air
7
Core[2 marks]

Explain why loft insulation reduces energy loss from a house.

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Method: Trapped air.

It traps air, reducing conduction and convection through the roof
8
Core[2 marks]

Explain why cavity wall insulation reduces energy loss.

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Method: Stops convection in cavity.

It fills the gap with foam that traps air, preventing convection currents in the cavity
9
Core[2 marks]

Explain why a metal tray of ice cubes melts ice faster than a plastic tray.

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Method: Metal conducts energy from the surroundings.

Metal conducts energy from the surroundings to the ice faster
10
Core[2 marks]

Explain why a thick duvet keeps you warm at night.

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Method: Traps air.

It traps air, a poor conductor, and prevents convection
11
Core[2 marks]

Explain why aluminium foil is wrapped around food to keep it hot.

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Method: Shiny surface.

The shiny surface is a poor emitter of infrared and reflects it back
12
Core[2 marks]

Explain why a hot water tank has a foam jacket.

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Method: Insulation.

The foam traps air, reducing conduction and convection, so less energy is lost
13
Core[2 marks]

Explain why a metal saucepan has a copper base.

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Method: Good conductor.

Copper conducts energy quickly from the hob to the food
14
Core[2 marks]

Explain how an oven heats food by convection.

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Method: Hot air circulates.

Air heated by the elements rises and circulates, transferring energy to the food
15
Core[2 marks]

Explain why a grill heats food mainly by radiation.

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Method: Element above.

The hot element above emits infrared radiation directly onto the food (hot air rises away from the food)
16
Core[2 marks]

Explain why curtains reduce energy loss through windows at night.

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Method: Trap air.

They trap a layer of air, reducing convection and conduction
17
Core[2 marks]

Explain why draught excluders reduce energy loss from a house.

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Method: Stop convection.

They stop warm air escaping and cold air entering by convection
18
Core[2 marks]

Explain why a lid on a hot drink keeps it warm longer.

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Method: Reduce convection and evaporation.

It reduces energy loss by convection and evaporation
19
Core[2 marks]

Explain why a tea cosy keeps a teapot hot.

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Method: Trapped air.

It traps air, a poor conductor, around the pot
20
Core[2 marks]

State the main method of thermal energy transfer through a solid wall.

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Method: Conduction.

Conduction
21
Core[2 marks]

State the main method of thermal energy transfer from the Sun to the Earth.

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Method: Radiation.

Radiation (infrared and light)
22
Core[2 marks]

Explain why the cooling unit of a freezer is at the top.

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Method: Convection.

Cold air sinks, setting up a convection current
23
Core[2 marks]

Explain why marshmallows on a stick held above a campfire cook mainly by convection, while those held to the side cook by radiation.

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Method: Hot gases rise.

Hot gases rise above the fire, carrying energy upwards; to the side only radiation reaches them
24
Core[2 marks]

Explain why a wooden spoon is used for stirring hot soup.

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Method: Poor conductor.

Wood is a poor conductor so the handle stays cool
25
Extended[3 marks]

Explain how a coal or wood fire heats a room by more than one method.

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Method: Radiation and convection.

Infrared radiation heats objects in front of the fire; hot air rises and sets up convection currents; conduction through the hearth
26
Extended[3 marks]

Explain how a car radiator keeps the engine cool.

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Method: Conduction, convection, radiation.

Hot coolant conducts energy into the metal fins; air flowing past carries energy away by convection; fins also emit infrared
27
Extended[2 marks]

Explain why car radiators have many thin fins.

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Method: Large surface area.

Large surface area increases the rate of energy transfer by convection and radiation
28
Extended[2 marks]

Explain why car radiators are often painted black.

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Method: Good emitter.

Black surfaces are good emitters of infrared radiation
29
Extended[3 marks]

Explain how a vacuum flask keeps a drink hot by reducing all three types of thermal energy transfer.

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Method: Vacuum, silvering, stopper.

Vacuum stops conduction and convection; silvered walls reduce radiation; stopper reduces convection and evaporation
30
Extended[2 marks]

Explain why someone sitting in front of a fire feels warm on the side facing it.

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Method: Radiation.

Infrared radiation travels directly from the fire and is absorbed by their skin
31
Extended[2 marks]

Explain why most of the energy from a fire goes up the chimney.

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Method: Convection.

Hot gases are less dense and rise up the chimney by convection
32
Extended[3 marks]

Explain why the inside of a parked car becomes very hot on a sunny day.

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Method: Radiation absorbed; trapped air.

Infrared and light enter through the windows and are absorbed by the interior; the warm air cannot escape by convection
33
Extended[3 marks]

Explain how a solar water panel transfers energy to the water.

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Method: Absorb, conduct, convect.

Dull black surfaces absorb infrared; energy is conducted through metal pipes to the water; heated water circulates by convection or a pump
34
Extended[3 marks]

Explain why a car engine needs a cooling system involving all three types of thermal energy transfer.

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Method: Remove energy.

Energy is conducted from the engine to the coolant, carried to the radiator by circulation (convection), then lost to air by convection and radiation
35
Extended[3 marks]

Explain three features of a vacuum flask that reduce energy transfer.

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Method: Vacuum, silvering, stopper.

Vacuum prevents conduction and convection; silvered surfaces reduce radiation; the insulating stopper reduces conduction, convection and evaporation
36
Extended[2 marks]

Explain why heat sinks on computer chips have many fins.

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Method: Surface area.

Large surface area increases energy transfer to the air by convection and radiation
37
Extended[3 marks]

Explain how a convector radiator heats a room although it is called a radiator.

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Method: Mostly convection.

Most energy is transferred by convection currents of air passing over it; only a small part is radiated
38
Extended[2 marks]

Explain why a hot bath cools faster without bubbles on the surface.

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Method: Bubbles reduce evaporation/convection.

A layer of bubbles traps air and reduces evaporation and convection from the surface
39
Extended[2 marks]

Explain why penguins huddle together in cold weather.

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Method: Reduce surface area.

Less of each penguin's surface is exposed, reducing energy loss
40
Extended[2 marks]

Explain why a thermos keeps cold drinks cold as well as hot drinks hot.

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Method: Reduces transfer either way.

It reduces energy transfer in both directions

Challenge questions

Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.

41
ChallengeCore[4 marks]

A pan of water is heated on an electric hob. Describe how energy reaches the top of the water, naming each method.

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Method: Conduction then convection.

Conduction from the hob through the metal base; convection currents carry energy through the water; some energy is lost from the surface by evaporation and radiation
42
ChallengeCore[4 marks]

Explain how a radiator heats a room by both convection and radiation, and which method is more important.

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Method: Mostly convection.

It emits infrared that warms nearby objects; air passing over it heats and rises, forming convection currents; convection transfers most of the energy
43
ChallengeCore[3 marks]

Explain why a cup of tea cools faster without a lid.

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Method: Convection and evaporation.

Hot air rises from the surface carrying energy away and water evaporates; a lid reduces both
44
ChallengeExtended[5 marks]

Explain the features of a vacuum flask that reduce conduction, convection and radiation, and explain why it eventually still cools.

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Method: Each feature.

Vacuum stops conduction and convection between walls; silvered surfaces reduce radiation; stopper reduces convection/evaporation. Energy still leaks by conduction through the stopper and the glass at the neck, and by slight radiation
45
ChallengeExtended[4 marks]

Explain how a car radiator keeps the engine at a safe temperature, mentioning all three types of energy transfer.

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Method: Coolant loop.

Energy is conducted from the engine to the coolant, carried by the pumped coolant to the radiator, conducted through the metal fins, and lost to the air by convection (fan) and radiation
46
ChallengeExtended[4 marks]

Explain why a solar water heater has a glass cover, a black absorbing plate and insulation behind it.

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Method: Each feature.

The black plate absorbs infrared; the glass reduces convection losses from the plate; insulation reduces conduction losses from the back
47
ChallengeExtended[4 marks]

A house loses energy through walls, roof, windows, floor and draughts. Suggest one improvement for each and the method of transfer it reduces.

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Method: Insulation methods.

Walls: cavity foam (convection/conduction); roof: loft insulation (conduction/convection); windows: double glazing (conduction/convection); floor: carpet/underlay (conduction); draughts: draught strips (convection)
48
ChallengeExtended[3 marks]

Explain why a house in a hot climate may have thick walls, small windows and white paint.

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Method: Reduce gain.

Thick walls slow conduction; small windows reduce radiation entering; white paint reflects infrared
49
ChallengeExtended[4 marks]

Explain why computer processors have metal heat sinks with fins and a fan.

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Method: Conduction, convection, area.

Metal conducts energy away from the chip; fins increase surface area; the fan increases convection to remove energy faster
50
ChallengeExtended[4 marks]

Explain why a campfire warms the side of your body facing it but not your back, and why you feel warm above the fire even without facing it.

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Method: Radiation and convection.

Radiation travels in straight lines from the fire to the facing side; above the fire hot gases rise by convection and transfer energy to you
All IGCSE Physics topics← 2.3.3 Radiation3.1 General Properties of Waves →

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