OxfordAQA International GCSE Physics: Kinetic theory, specific heat and latent heat, conduction, convection and expansion (9203) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sections 3.4.1 and 3.4.2 of the OxfordAQA International GCSE Physics (9203) specification, for exams from May/June 2018. Where a question needs a value, it is given: use c for water = 4200 J/kg °C, LF for water = 3.34 × 10⁵ J/kg and LV for water = 2.26 × 10⁶ J/kg unless told otherwise. Read the study guide first if a topic is new, and use the revision notes for recall. See also the OxfordAQA International GCSE Physics hub, the printable checklist and the free diagnostics.

Questions

1. For each of the three states of matter, describe how the particles are arranged and how they move. [3]

2. A 3.2 kg iron block, with specific heat capacity 450 J/kg °C, cools from 85 °C to 25 °C.

(a) Calculate the energy transferred from the block. [2] (b) Explain why the block cools more slowly as it approaches 25 °C. [2]

3. A student heats a 0.80 kg metal block with a 45 W heater for 8.0 minutes. The temperature rises from 19.0 °C to 49.0 °C.

(a) Calculate the energy supplied by the heater. [2] (b) Calculate the specific heat capacity of the metal. [2] (c) The true value is lower than the student’s value. Explain why, and suggest one improvement. [2]

4. A 1.5 kW heater melts 0.60 kg of ice at 0 °C. Assume no energy is lost.

(a) Calculate the energy needed. [2] (b) Calculate the time taken. [2] (c) Explain why the temperature stays at 0 °C while the ice melts. [1]

5. Steam of mass 0.045 kg at 100 °C condenses to water at 100 °C.

(a) Calculate the energy released. [2] (b) All of this energy warms 0.50 kg of water. Calculate the temperature rise. [2] (c) Explain why a burn from steam is worse than a burn from the same mass of boiling water. [2]

6. Stearic acid is cooled from a liquid. Its temperature is recorded every minute.

Time (min)	0	1	2	3	4	5	6	7	8	9
Temperature (°C)	80	76	72	69	69	69	69	66	63	60

(a) State the freezing point of stearic acid from the data. [1] (b) State the times between which it was freezing. [1] (c) Explain why the temperature is constant while it freezes. [2] (d) Calculate the average rate of cooling from 0 to 2 minutes and from 7 to 9 minutes, and explain the difference. [3] (e) Describe how the curve would differ for a sample containing an impurity. [2]

7. A 500 W heater warms 0.20 kg of liquid. The liquid boils from 4.0 minutes to 10.0 minutes, with its temperature constant.

(a) Calculate the energy supplied during boiling. [2] (b) Calculate the specific latent heat of vaporisation. [2] (c) Explain what the energy does during boiling. [2] (d) State why the student’s value is likely to be too high. [1]

8. (a) Salt is spread on icy roads. Explain why this helps. [2] (b) A liquid is said to boil at 100 °C if pure. A sample boils gradually between 102 °C and 106 °C. What does this suggest? [2]

9. (a) A metal spoon and a plastic spoon stand in hot soup. Explain, in terms of particles, why the metal handle becomes warm faster. [3] (b) An immersion heater is fixed near the bottom of a water tank. Explain how the water at the top becomes hot. [3]

10. (a) Explain, using kinetic theory, why a puddle of water cools as it evaporates. [3] (b) State two changes that would make wet washing dry faster. [2]

11. A cuboid measures 3 cm by 4 cm by 5 cm. A larger cuboid of the same shape measures 6 cm by 8 cm by 10 cm.

(a) Find the ratio of surface area to volume for the smaller cuboid. [3] (b) Find the same ratio for the larger cuboid. [2] (c) Explain why animals in cold regions tend to have compact bodies and small ears. [3]

12. (a) Describe how a bi-metallic strip thermostat switches off a heater when a room becomes too warm. [4] (b) Explain why a steel bridge is built with expansion gaps. [1]

Answers

1. Solid: particles touch, in a regular pattern, and vibrate about fixed positions [1]. Liquid: particles touch with no pattern and move around each other [1]. Gas: particles are far apart, random, and move quickly in all directions [1]. [3] Examiner insight: Give spacing, pattern and movement for each state; saying only “close together” for both solid and liquid cannot separate them.

2. (a) Δθ = 85 − 25 = 60 °C [1]. E = 3.2 × 450 × 60 = 86 400 J (8.6 × 10⁴ J) [1] (b) The temperature difference between block and room falls [1], so the rate of energy transfer by heating falls [1]. [4] Examiner insight: Write the equation, the substitution and the unit; a bare wrong number leaves nothing to reward.

3. (a) t = 8.0 × 60 = 480 s [1]. E = 45 × 480 = 21 600 J [1] (b) Δθ = 30 °C [1]. c = 21 600 / (0.80 × 30) = 900 J/kg °C [1] (c) Some energy is lost to the surroundings, so less than 21 600 J warmed the block [1]. Wrap the block in insulation (lagging) [1]. [6] Examiner insight: Say which way the error goes and why; “human error” is not an explanation.

4. (a) E = 0.60 × 3.34 × 10⁵ [1] = 200 400 J (2.0 × 10⁵ J) [1] (b) t = 200 400 / 1500 [1] = 133.6 s = 130 s (2 s.f.) [1] (c) The energy supplied breaks the ordered arrangement and separates particles rather than increasing their kinetic energy [1]. [5] Examiner insight: Linking the plateau to energy changing particle separation, not kinetic energy, is the point; “it has reached its melting point” repeats the question.

5. (a) E = 0.045 × 2.26 × 10⁶ [1] = 101 700 J (1.0 × 10⁵ J) [1] (b) Δθ = E / (m c) = 101 700 / (0.50 × 4200) [1] = 48.4, so 48 °C [1] (c) Steam releases latent heat when it condenses [1], in addition to the energy released as the water then cools [1]. [6] Examiner insight: Keep the mass in kilograms (0.045, not 45) and watch for slips of powers of ten.

6. (a) 69 °C [1] (b) 3 to 6 minutes [1] (c) Particles come together and form bonds, releasing energy [1]; this replaces the energy transferred to the surroundings, so the kinetic energy and temperature do not fall [1]. (d) 0 to 2 min: (80 − 72) / 2 = 4.0 °C/min [1]. 7 to 9 min: (66 − 60) / 2 = 3.0 °C/min [1]. The sample is closer to room temperature later, so the temperature difference is smaller and it transfers energy more slowly [1]. (e) The plateau would be at a lower temperature [1] and the temperature would fall over a range instead of staying constant [1]. [9] Examiner insight: For a rate question, show both subtractions and the division; an explanation that mentions temperature difference earns credit only if it compares the two stages.

7. (a) t = (10.0 − 4.0) × 60 = 360 s [1]. E = 500 × 360 = 180 000 J [1] (b) L = E / m = 180 000 / 0.20 [1] = 9.0 × 10⁵ J/kg [1] (c) It increases the potential energy of the particles as they separate [1]; it does not increase their kinetic energy, so the temperature is constant [1]. (d) Some of the energy was lost to the surroundings, so less than 180 000 J evaporated the liquid [1]. [7] Examiner insight: Convert minutes to seconds before using power times time, and show it.

8. (a) Salt dissolves in the water on the ice and lowers its freezing (melting) point [1], so the water stays liquid below 0 °C and the ice melts [1]. (b) The sample is impure [1]; impurities raise the boiling point and cause a range of boiling temperatures [1]. [4] Examiner insight: “It is not pure” scores less than saying what impurities do to the temperature.

9. (a) Particles in the metal vibrate more where heated and pass energy on [1]. Free electrons in the metal carry energy through the handle quickly [1]. Plastic has no free electrons, so it conducts more slowly [1]. (b) The water near the heater warms and expands, so particles move apart and its density falls [1]. The warmer, less dense water rises [1], and cooler, denser water sinks to take its place, forming a convection current [1]. [6] Examiner insight: Mention density in a convection answer; “hot water rises” with no reason is incomplete.

10. (a) The fastest particles at the surface have enough energy to escape [1]. The average kinetic energy of the remaining particles falls [1], so the water cools [1]. (b) Any two: hang it in a warmer place; spread it out to increase surface area; hang it in a breeze; dry air [2]. [5] Examiner insight: Say that the fastest particles leave; “the liquid turns to a gas” does not explain the cooling.

11. (a) Surface area = 2 (12 + 15 + 20) = 94 cm² [1]. Volume = 3 × 4 × 5 = 60 cm³ [1]. Ratio = 94 / 60 = 1.6 per cm [1] (b) Surface area = 376 cm², volume = 480 cm³ [1]; ratio = 0.78 per cm [1] (c) A compact body with small ears has a low surface area to volume ratio [1]. Less area means a slower rate of energy transfer to the surroundings [1], which helps the animal stay warm [1]. [8] Examiner insight: Compare the two ratios in words (halved when each length doubles); a calculation with no comment is incomplete.

12. (a) The strip is two metals joined together that expand by different amounts [1]. When the room warms, the strip bends [1] away from the contact, breaking the circuit [1] and switching the heater off. As it cools, the strip straightens and the heater switches on [1]. (b) The steel expands when hot; the gaps stop it buckling [1]. [5] Examiner insight: State which way the strip bends and what that does to the circuit.

Where marks are usually lost

• Using E = m c Δθ for the stage where the substance is changing state.
• Not converting minutes to seconds, or grams to kilograms.
• Writing a number without the unit.
• Saying a flat part of a graph means energy stops being supplied.
• Describing particles as “getting hot” instead of moving faster.
• Writing “heat rises” without density and particle spacing.
• Leaving out the free electrons when explaining conduction in a metal.
• Saying evaporation cools “because heat is lost” without the loss of the fastest particles.

Next steps

• Read the revision notes and the study guide.
• Go to the course hub and tick this topic off on the checklist.
• Take the free 10-minute diagnostics to see what to revise next.
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Official syllabus

These questions are aligned to sections 3.4.1 and 3.4.2 of the OxfordAQA International GCSE Physics (9203) specification, for exams May/June 2018 onwards, published by OxfordAQA.