Focused revision

Thermal Physics revision guide

Use the skill selected by your revision plan. Work in order: understand the idea, study the example, check the common mistake, practise it, then check again in 7 days.

Focused skill

States and particle model

1. Explain

Compare physical properties by linking them to particle arrangement, motion, separation and forces; the particles themselves do not expand, melt or disappear.

2. Model

Solid particles are close and ordered around fixed positions; gas particles are far apart and move rapidly at random.

3. Practise: concept check

Do particles grow when a solid expands on heating?

No; their average separation changes.
Yes; each particle becomes larger.

Check the answer and feedback

Correct: No; their average separation changes. The model changes spacing and motion, not particle identity or size.

Not yet: The model changes spacing and motion, not particle identity or size.

4. Apply: examiner-style practice

Compare the volume and compressibility of a liquid and a gas using particle separation.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: A liquid has nearly fixed volume and is hard to compress because its particles are close.My response includes the correct unit.
1 mark: A gas fills its container and compresses easily because large gaps separate its particles.My response includes the correct unit.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Brownian-motion evidence

1. Explain

A Brownian experiment directly shows a larger suspended particle moving irregularly; infer unseen random molecular motion from unequal impacts.

2. Model

A visible smoke particle repeatedly changes direction because different numbers of air molecules strike it from different sides.

Brownian-motion evidence investigation

Predict: Predict how a visible suspended particle moves when molecular impacts are unequal.
Change: Compare particle paths while changing temperature separately.
Observe: Record direction changes over equal time intervals.
Interpret: Separate the observed suspended particle from the unseen molecular motion inferred from it.
Limitation: A two-dimensional display is not a literal microscope view and does not show true molecular scale.
Transfer: Write an observation-and-inference answer for a smoke-cell experiment.

Open the activity

3. Practise: concept check

Can individual air molecules be seen in the school experiment?

No; their motion is inferred from the visible particle.
Yes; each bright point is one air molecule.

Check the answer and feedback

Correct: No; their motion is inferred from the visible particle. Distinguish observation from the molecular inference.

Not yet: Distinguish observation from the molecular inference.

4. Apply: examiner-style practice

Describe the observation and inference in a smoke-cell Brownian motion experiment.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Observe illuminated smoke particles following irregular zigzag paths.
1 mark: Infer that unseen air molecules move continuously and randomly and collide unevenly with them.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Temperature and gas pressure

1. Explain

A temperature rise means greater average particle kinetic energy. Gas pressure is the wall force per area produced by repeated particle collisions and momentum changes.

2. Model

At fixed volume, heating makes particles faster, so wall collisions are more frequent and involve greater momentum change.

Gas-pressure particle investigation

Predict: Predict pressure change when temperature rises at fixed volume.
Change: Vary temperature and volume separately.
Observe: Record collision rate or pressure after the model settles.
Interpret: Connect molecular speed and collision frequency to wall force.
Limitation: A two-dimensional idealised display is not a literal gas sample.
Transfer: Explain a bicycle-pump pressure change using collision reasoning.

Open the activity

3. Practise: concept check

Does heating a sealed gas create more particles?

No; existing particles move faster.
Yes; new particles create the pressure.

Check the answer and feedback

Correct: No; existing particles move faster. Explain pressure using motion and collisions rather than particle creation.

Not yet: Explain pressure using motion and collisions rather than particle creation.

4. Apply: examiner-style practice

Explain why compressing a gas at constant temperature increases pressure.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Particles travel a shorter distance between wall collisions, so collisions become more frequent.
1 mark: Average speed remains constant at constant temperature, but the wall force per area increases.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Heating and thermal equilibrium

1. Explain

Energy transfers by heating from higher to lower temperature until both regions reach the same temperature and there is no net transfer.

2. Model

A cold spoon in hot tea gains energy while the tea loses energy until their temperatures become equal.

3. Practise: concept check

Must objects in thermal equilibrium have equal internal energy?

No; they need equal temperature.
Yes; every energy store must be equal.

Check the answer and feedback

Correct: No; they need equal temperature. Temperature equality, not equal mass or internal energy, defines equilibrium.

Not yet: Temperature equality, not equal mass or internal energy, defines equilibrium.

4. Apply: examiner-style practice

A hot block and a cooler block touch in an insulated box. Describe the transfer and final condition.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Energy transfers from the hotter block to the cooler block.
1 mark: Transfer continues until their temperatures are equal and net energy transfer stops.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Conduction in solids

1. Explain

Solid particles transfer energy through vibrations and interactions while remaining about fixed positions; mobile electrons provide an additional rapid mechanism in metals.

2. Model

A metal spoon conducts faster than wood because energetic mobile electrons carry energy through its lattice.

3. Practise: concept check

Do hot particles travel along a solid spoon?

No; energy passes through interactions and electrons.
Yes; particles flow from the hot end.

Check the answer and feedback

Correct: No; energy passes through interactions and electrons. Do not confuse conduction with bulk fluid motion.

Not yet: Do not confuse conduction with bulk fluid motion.

4. Apply: examiner-style practice

Explain why a metal pan has a metal base but a polymer handle.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: The metal base conducts energy rapidly to the food through lattice interactions and mobile electrons.
1 mark: The polymer is a poor conductor, reducing energy transfer to the hand.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Density-driven convection

1. Explain

Convection is bulk fluid motion caused by density differences: a heated region expands, becomes less dense and rises while cooler denser fluid replaces it.

2. Model

Air above a heater rises and cooler air moves in, forming a continuous circulation.

Convection investigation

Predict: Predict the circulation direction when a fluid is heated from below.
Change: Change heater position while holding the fluid and container fixed.
Observe: Record rising and sinking regions in each case.
Interpret: Link bulk motion to temperature-dependent density differences and replacement flow.
Limitation: The model simplifies viscosity and three-dimensional turbulence.
Transfer: Explain one ventilation or sea-breeze pattern using density changes.

Open the activity

3. Practise: concept check

Is ‘heat rises’ a complete explanation?

No; state the density change and replacement flow.
Yes; heat is a rising substance.

Check the answer and feedback

Correct: No; state the density change and replacement flow. Convection needs a fluid, a density difference and bulk movement.

Not yet: Convection needs a fluid, a density difference and bulk movement.

4. Apply: examiner-style practice

Explain how a sea breeze develops during the day.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Air over warmer land heats, expands, becomes less dense and rises.
1 mark: Cooler denser air from above the sea moves towards land to replace it, completing circulation.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Radiation and applications

1. Explain

Electromagnetic radiation needs no medium. Its transfer rate depends on surface colour and texture, surface temperature and surface area; applications often combine all three processes.

2. Model

A vacuum flask uses silvered walls against radiation and a vacuum against conduction and convection.

Thermal-transfer comparison

Predict: Predict which surface and insulation combination cools slowest.
Change: Change surface finish and insulation while keeping starting temperature fixed.
Observe: Record temperature at equal time intervals for repeat runs.
Interpret: Separate radiation effects from conduction and convection controls.
Limitation: Room conditions and sensor lag would vary in a real experiment.
Transfer: Evaluate one design feature of a vacuum flask.

Open the activity

3. Practise: concept check

Does a vacuum stop infrared radiation?

No; electromagnetic radiation crosses empty space.
Yes; every thermal process needs particles.

Check the answer and feedback

Correct: No; electromagnetic radiation crosses empty space. Match each design feature to the process it changes.

Not yet: Match each design feature to the process it changes.

4. Apply: examiner-style practice

Explain how two features of a solar water heater improve performance.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: A dull black collector is a strong radiation absorber.My response includes the correct unit.
1 mark: A transparent cover admits radiation while reducing convection from the warm collector.My response includes the correct unit.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Internal energy

1. Explain

Internal energy is the total random kinetic energy of particles plus their total potential energy; temperature relates to average kinetic energy, not this total store.

2. Model

Equal-temperature blocks can have different internal energy if their mass, material or state differs.

3. Practise: concept check

Does equal temperature imply equal internal energy?

No; internal energy is a total that also depends on the system.
Yes; temperature measures total energy.

Check the answer and feedback

Correct: No; internal energy is a total that also depends on the system. Separate average kinetic energy from the total microscopic store.

Not yet: Separate average kinetic energy from the total microscopic store.

4. Apply: examiner-style practice

Explain how internal energy changes while ice melts at constant temperature.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Average particle kinetic energy and temperature remain constant.
1 mark: Particle potential energy and total internal energy increase as the arrangement changes.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Heat capacity and specific heat capacity

1. Explain

Heat capacity is energy per unit temperature rise for an object; specific heat capacity is energy per unit mass per unit temperature rise. Apply Q = mcΔθ.

2. Model

0.40 kg of aluminium with c = 900 J/(kg °C) warmed by 15 °C needs 5400 J.

3. Practise: concept check

Should final temperature replace Δθ in Q = mcΔθ?

No; use the temperature change.
Yes; use whichever temperature is larger.

Check the answer and feedback

Correct: No; use the temperature change. Convert mass to kilograms and calculate the change explicitly.

Not yet: Convert mass to kilograms and calculate the change explicitly.

4. Apply: examiner-style practice

A 250 W heater warms 0.50 kg of water by 12 °C. With c = 4200 J/(kg °C), find ideal heating time.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Q = mcΔθ = 25 200 J.My response includes the correct unit.
1 mark: t = Q/P = 100.8 s, about 101 s.My response includes the correct unit.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Changes of state and evaporation

1. Explain

Melting, solidification, boiling and condensation occur at constant temperature for a pure substance at fixed pressure. Evaporation is a surface process possible at any temperature.

2. Model

During boiling, bubbles form throughout the liquid; during evaporation, higher-energy surface particles escape.

3. Practise: concept check

Are boiling and evaporation identical?

No; location and temperature conditions differ.
Yes; both occur only at boiling point.

Check the answer and feedback

Correct: No; location and temperature conditions differ. State both the location and temperature distinctions.

Not yet: State both the location and temperature distinctions.

4. Apply: examiner-style practice

Compare boiling with evaporation and explain evaporative cooling.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Boiling occurs throughout at a fixed temperature; evaporation occurs at the surface at any temperature.
1 mark: Higher-energy surface particles escape, lowering the average kinetic energy of those remaining.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Latent heat and particles

1. Explain

Latent heat is energy transferred during a change of state without temperature change; specific latent heat is energy per unit mass. Apply Q = ml.

2. Model

Melting 0.30 kg with l = 2.0 × 10⁵ J/kg requires 6.0 × 10⁴ J while particle potential energy increases.

3. Practise: concept check

Does constant temperature mean zero energy transfer?

No; latent energy changes particle potential energy.
Yes; no energy enters during a plateau.

Check the answer and feedback

Correct: No; latent energy changes particle potential energy. Average kinetic energy can stay constant while internal energy changes.

Not yet: Average kinetic energy can stay constant while internal energy changes.

4. Apply: examiner-style practice

A 600 W heater vaporises 0.15 kg in 180 s at boiling point. Estimate specific latent heat.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Energy supplied = Pt = 108 000 J.My response includes the correct unit.
1 mark: l = Q/m = 7.2 × 10⁵ J/kg.My response includes the correct unit.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.

Focused skill

Cooling curves

1. Explain

A cooling curve shows temperature against time. Slopes represent cooling within one state; plateaux represent constant-temperature changes of state with two states present.

2. Model

A freezing plateau lasts while latent energy leaves and particles form a more ordered arrangement without changing average kinetic energy.

Cooling-curve practical

Predict: Predict where a plateau appears and what happens to internal energy there.
Change: Use a fixed mass and cooling environment; compare repeat cooling curves.
Observe: Record temperature at regular intervals through the state change.
Interpret: Identify the plateau and relate its duration to latent energy transfer.
Limitation: Heat loss rate is not constant and supercooling may occur.
Transfer: Explain why a larger sample may show a longer plateau.

Open the activity

3. Practise: concept check

Does a plateau mean cooling has stopped?

No; energy continues to leave during the state change.
Yes; no energy leaves because temperature is fixed.

Check the answer and feedback

Correct: No; energy continues to leave during the state change. Interpret energy and state as well as graph shape.

Not yet: Interpret energy and state as well as graph shape.

4. Apply: examiner-style practice

Sketch and label a cooling curve for a gas that condenses and then freezes.

[2 marks]

Self-mark with the mark scheme

Compare your response with each mark point. Select a point only when your response contains that evidence.

Award a mark only when the stated physics matches the mark point. Carry forward a correct method after an arithmetic slip; do not award a bare answer where reasoning is requested.

Mark points

1 mark: Show falling-temperature regions separated by two horizontal plateaux, with time on the horizontal axis and temperature on the vertical axis.
1 mark: Label gas, gas-liquid condensation, liquid, liquid-solid freezing and solid regions in order.

5. Check again in 7 days: return through Your Physics plan after seven days. You will get a different question and cannot complete it early.