IGCSE Physics Thermal Expansion of Solids, Liquids and Gases Questions and Worked Solutions (2.2.1) | 0625

By /
IGCSE Physics 0625 · Topic 2.2.1

IGCSE Physics Thermal Expansion of Solids, Liquids and Gases Questions and Worked Solutions

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

50 questions28 Core12 Extended10 Challenge114 marksTextbook §2.2 · pp. 100–114
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: Thermal Expansion of Solids, Liquids and Gases

Most substances expand when heated and contract when cooled. Gases expand most and solids least. Thermal expansion is useful (thermometers, thermostats) but can cause problems (buckled rails, cracked bridges).

Key formulas

No equations to learn in this subtopic — order of expansion: gas > liquid > solid.

Prerequisite knowledge

  • Particle model (2.1.2)
  • States of matter (2.1.1)

Exam tips & common mistakes

  • Mass does not change on expansion; volume increases so density decreases
  • For bimetallic strips, say which metal ends up on the outside
  • Link the order of expansion to the strength of forces between particles

Key facts from the syllabus (2.2.1)

  • Solids, liquids and gases expand when heated; gases expand the most
  • Applications: liquid-in-glass thermometers, bimetallic strips in thermostats and fire alarms, fitting metal tyres
  • Problems: railway lines buckling, bridges and pavements cracking, overhead cables snapping in cold weather — solved with gaps and expansion joints
  • A bimetallic strip bends because two metals expand by different amounts; the metal that expands more is on the outside of the curve
  • Extended particles move faster and further apart; weak forces in gases allow the most expansion

Textbook: §2.2 Thermal properties and temperature, pp. 100–114

1
Core[1 mark]

State what happens to most materials when they are heated.

Show solutionHide solution

Method: They expand.

They expand
2
Core[1 mark]

State which state of matter expands the most for the same temperature rise.

Show solutionHide solution

Method: Gases.

Gas
3
Core[1 mark]

State which state of matter expands the least for the same temperature rise.

Show solutionHide solution

Method: Solids.

Solid
4
Core[2 marks]

Explain why gaps are left between sections of railway track.

Show solutionHide solution

Method: Expansion on hot days.

To allow the rails to expand on hot days without buckling
5
Core[2 marks]

Explain why overhead power cables are left slack in summer.

Show solutionHide solution

Method: Contract in winter.

They contract in cold weather; slack prevents them snapping
6
Core[2 marks]

Explain how a liquid-in-glass thermometer works.

Show solutionHide solution

Method: Liquid expands up the tube.

As temperature rises, the liquid expands and rises up the narrow tube against a scale
7
Core[2 marks]

A metal lid is stuck on a glass jar. Explain why running hot water over the lid helps.

Show solutionHide solution

Method: Metal expands more than glass.

The metal lid expands more than the glass, loosening it
8
Core[2 marks]

Describe how a bimetallic strip bends when heated.

Show solutionHide solution

Method: Two metals expand differently.

It bends towards the metal that expands less (the more-expanding metal is on the outside of the curve)
9
Core[1 mark]

Give one use of a bimetallic strip.

Show solutionHide solution

Method: Thermostat.

Thermostat (or fire alarm, or thermal switch)
10
Core[2 marks]

Explain why bridges have expansion joints.

Show solutionHide solution

Method: Expansion and contraction with temperature.

To let the bridge expand and contract with temperature changes without cracking
11
Core[2 marks]

A full bottle of water is left in a hot car and leaks. Explain why.

Show solutionHide solution

Method: Liquid expands.

The water expands when heated and the pressure forces liquid out
12
Core[2 marks]

A balloon placed in a freezer shrinks. Explain why.

Show solutionHide solution

Method: Gas contracts on cooling.

The gas contracts when cooled (particles slow, pressure drops) so the volume decreases
13
Core[2 marks]

Explain why concrete pavements are laid in sections with gaps.

Show solutionHide solution

Method: Expansion.

To allow for expansion in hot weather so the slabs do not crack
14
Core[1 mark]

State one problem caused by thermal expansion.

Show solutionHide solution

Method: e.g. buckling.

e.g. railway lines buckle, bridges crack, cables snap in cold
15
Core[2 marks]

Explain why a glass dish may crack if boiling water is poured into it.

Show solutionHide solution

Method: Uneven expansion.

The inside expands faster than the outside, causing stress that cracks the glass
16
Core[2 marks]

Explain why telephone wires sag more in summer than in winter.

Show solutionHide solution

Method: Expansion.

The wires expand and become longer in hot weather
17
Core[2 marks]

Explain how a fire alarm using a bimetallic strip works.

Show solutionHide solution

Method: Strip bends to close circuit.

Heat makes the strip bend, closing a circuit that rings the bell
18
Core[2 marks]

Explain how a thermostat using a bimetallic strip switches off a heater.

Show solutionHide solution

Method: Bends away from contact.

When hot, the strip bends away from a contact, breaking the circuit; when it cools it reconnects
19
Core[2 marks]

A brass and an iron strip are riveted together; brass expands more. State which way it bends when heated.

Show solutionHide solution

Method: Brass on outside.

It bends with the brass on the outside of the curve (towards the iron)
20
Core[2 marks]

State what happens to the bimetallic strip in the previous question when it is cooled below room temperature.

Show solutionHide solution

Method: Opposite bend.

It bends the other way, with brass on the inside
21
Core[2 marks]

Explain why a steel tyre can be fitted tightly onto a wheel by heating it first.

Show solutionHide solution

Method: Expand then contract.

Heating expands the tyre so it fits over the wheel; on cooling it contracts and grips tightly
22
Core[2 marks]

Explain why pipes carrying hot liquids in factories have bends or loops.

Show solutionHide solution

Method: Allow expansion.

The loops allow the pipes to expand and contract without breaking
23
Core[2 marks]

Explain why the liquid level in a thermometer drops slightly when first placed in hot water before rising.

Show solutionHide solution

Method: Glass expands first.

The glass bulb heats and expands first, increasing its volume before the liquid heats and expands
24
Core[2 marks]

State why mercury or alcohol is used in thermometers rather than water.

Show solutionHide solution

Method: Uniform expansion, range.

They expand evenly over a wide range of temperatures and are visible; water freezes at 0 °C
25
Core[2 marks]

Explain why a gap is left at the top of a bottle of fizzy drink.

Show solutionHide solution

Method: Expansion.

To allow the liquid to expand if it warms, without bursting the bottle
26
Core[2 marks]

State one useful application and one problem caused by thermal expansion.

Show solutionHide solution

Method: Examples.

Useful: thermostat/thermometer/riveting. Problem: buckling of rails or roads
27
Core[2 marks]

Explain why the tops of concrete roads have tar between slabs.

Show solutionHide solution

Method: Expansion gaps.

The tar fills expansion gaps and is squeezed as the slabs expand
28
Core[2 marks]

A tight metal ring is hard to remove from a metal rod. Suggest how to remove it using thermal effects.

Show solutionHide solution

Method: Heat ring/cool rod.

Heat the ring (so it expands) or cool the rod (so it contracts)
29
Extended[3 marks]

Explain, in terms of particles, why solids expand when heated.

Show solutionHide solution

Method: Particles vibrate more, average separation increases.

Particles vibrate with larger amplitude, so they take up more space and the average separation increases
30
Extended[3 marks]

Explain, in terms of particles, why gases expand much more than solids for the same temperature rise.

Show solutionHide solution

Method: Weak forces in gases.

Gas particles have negligible forces between them so they move apart freely; strong forces in solids restrict separation
31
Extended[2 marks]

Explain why liquids expand more than solids but less than gases.

Show solutionHide solution

Method: Intermediate forces.

Forces between liquid particles are weaker than in solids but stronger than in gases
32
Extended[2 marks]

State the order of magnitude of expansion for solids, liquids and gases, from greatest to least.

Show solutionHide solution

Method: Gas > liquid > solid.

Gas > liquid > solid
33
Extended[2 marks]

Explain why a thermometer uses a narrow capillary tube.

Show solutionHide solution

Method: Small expansion gives large rise.

A small increase in liquid volume produces a large change in length, making it more sensitive
34
Extended[2 marks]

Explain why the mass of a metal bar does not change when it expands.

Show solutionHide solution

Method: Same particles.

The number of particles is the same; only their separation increases
35
Extended[2 marks]

Explain why gases expand much more than liquids when heated at constant pressure.

Show solutionHide solution

Method: Forces negligible.

Gas particles are not held together, so increased kinetic energy moves them much further apart
36
Extended[3 marks]

Explain why liquids expand when heated, in terms of particles and forces.

Show solutionHide solution

Method: Faster motion overcomes some attraction.

Particles gain kinetic energy and move faster, so they push slightly further apart against the attractive forces
37
Extended[2 marks]

Explain why solids expand only slightly when heated.

Show solutionHide solution

Method: Strong forces.

Strong forces hold the particles in place, so their mean separation increases only slightly
38
Extended[2 marks]

State the order of relative expansion of solids, liquids and gases for the same temperature rise, with a reason.

Show solutionHide solution

Method: Forces decide.

Gas > liquid > solid, because the forces between particles are weakest in gases and strongest in solids
39
Extended[2 marks]

Explain why the density of a substance decreases when it expands.

Show solutionHide solution

Method: Same mass, larger volume.

The mass stays the same but the volume increases, so density = m/V decreases
40
Extended[2 marks]

Explain why a hot air balloon uses heating rather than adding more air.

Show solutionHide solution

Method: Expansion reduces density.

Heating makes the air expand and become less dense than the surrounding air, so it rises

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 bimetallic strip of brass and steel (brass expands more) is used in a thermostat that switches a heater off when the room is warm. Explain how it works, including which way it bends.

Show solutionHide solution

Method: Bends with brass on outside.

As it warms, the brass expands more so the strip bends with brass on the outside, moving away from the contact and breaking the heater circuit; on cooling it straightens and reconnects
42
ChallengeCore[3 marks]

Explain why railway lines were traditionally laid with small gaps between sections, and what can happen on a very hot day without them.

Show solutionHide solution

Method: Expansion.

Rails expand in heat; without gaps they push against each other and buckle
43
ChallengeCore[3 marks]

A glass bottle with a tight metal lid is hard to open. Explain why running hot water over the lid helps, and why this would not help if the lid were glass too.

Show solutionHide solution

Method: Different expansion.

Metal expands more than glass so the lid loosens; if both were glass they would expand by similar amounts
44
ChallengeCore[4 marks]

Explain why a liquid-in-glass thermometer has a thin-walled bulb and a narrow capillary tube.

Show solutionHide solution

Method: Sensitivity.

The thin wall lets energy pass quickly so it responds fast; the narrow tube makes a small volume change produce a large change in length (more sensitive)
45
ChallengeCore[3 marks]

Explain why bridges are built with one end on rollers.

Show solutionHide solution

Method: Allow expansion.

The bridge can expand and contract with temperature without stressing or cracking the structure
46
ChallengeExtended[4 marks]

Explain, in terms of particles, why the same temperature rise causes much more expansion in a gas than in a solid.

Show solutionHide solution

Method: Forces between particles.

In a solid strong forces limit how far apart vibrating particles can move; in a gas there are negligible forces, so faster particles spread out much more
47
ChallengeExtended[4 marks]

Explain why water in a full kettle may overflow as it heats, even though no more water is added.

Show solutionHide solution

Method: Liquid expansion.

Liquid particles move faster and further apart, so the water's volume increases
48
ChallengeExtended[4 marks]

A steel rod and a glass rod of equal length are heated by the same amount. Explain why a thermometer made with a steel case could give errors.

Show solutionHide solution

Method: Different expansion.

The steel and glass expand by different amounts, changing the scale or tube volume and so the reading
49
ChallengeExtended[3 marks]

Explain why the density of most substances decreases as they are heated.

Show solutionHide solution

Method: Same mass, larger volume.

Mass stays constant while volume increases, so density decreases
50
ChallengeExtended[4 marks]

Explain how a hot-air balloon uses thermal expansion and density to rise.

Show solutionHide solution

Method: Expansion lowers density.

Heated air expands; some is pushed out, so the air inside is less dense than the cooler outside air, and the balloon rises
All IGCSE Physics topics← 2.1.3 Gases and the Absolute Scale of Temperature2.2.2 Specific Heat Capacity →

Book a free trial class

Tell us a little about your requirement.