IGCSE Physics 0625 Paper 4: Thermal Physics, Heat Transfer and Specific Heat Capacity

Level: Year 10-11 (IGCSE) | Subject: Chemistry 0620 | Time: 75 minutes | Total: 100 marks | Parts: 31

Paper at a glance

Paper	Time	Marks	Calculator
Paper 4 (Extended, structured)	1 h 15 min	75	Not allowed

Questions

Question 1 (16 marks) – The kinetic particle model and the three states of matter

(a) Describe the arrangement and the motion of particles in a solid, a liquid and a gas. (3 marks)

(b) Use the particle model to explain why a solid expands when it is heated. (3 marks)

(c) State the relationship between temperature and the average kinetic energy of gas particles. (2 marks)

(d) Explain how gas pressure is produced by the motion of particles. (3 marks)

(e) Explain why a liquid is difficult to compress while a gas is easy to compress. (2 marks)

(f) Explain why diffusion is faster in a gas than in a liquid. (3 marks)

Question 2 (17 marks) – Specific heat capacity and heating calculations

(a) Define specific heat capacity and explain what 4200 J/(kg°C) means for water. (3 marks)

(b) A container holds 0.50 kg of water which is heated from 20 C to 80 C. The specific heat capacity of water is 4200 J/(kg C). Calculate the energy absorbed by the water and give your answer in kJ. (4 marks)

(c) If a heater of power 1200 W is used and no energy is lost, calculate the time needed. (3 marks)

(d) In practice the supply delivers 1500 W. Calculate the total energy supplied and the efficiency of the heater. (4 marks)

(e) Explain why the air temperature at the coast is usually lower than inland during the day. (3 marks)

Question 3 (17 marks) – Melting, latent heat and cooling curves

(a) Explain why the temperature stays constant while ice melts even though energy is still being supplied. (3 marks)

(b) 0.20 kg of ice at 0 C is completely melted to water at 0 C. The specific latent heat of fusion of ice is 334000 J/kg. Calculate the energy needed. (4 marks)

(c) A heater of power 1200 W supplies this energy with no loss. Calculate the time taken for the ice to melt completely. (3 marks)

(d) Explain why ice at 0 C cools the skin more than the same mass of water at 0 C. (4 marks)

(e) Describe the temperature-time graph for ice being heated to steam and state the meaning of the two flat sections. (3 marks)

Question 4 (17 marks) – Conduction, convection and radiation

(a) Compare conduction, convection and radiation, stating which of them need a medium. (3 marks)

(b) A glass pane has thermal conductivity 0.50 W/(m K), area 0.020 m2 and thickness 0.010 m. The temperature difference across it is 20 C. Use Q/t = k A dT / d to calculate the energy conducted per second. (4 marks)

(c) Explain how double glazing reduces heat loss from a house. (3 marks)

(d) Explain how convection sets up a circulation in a kettle heated from below. (4 marks)

(e) Explain why dark surfaces absorb more radiation and give one everyday application. (3 marks)

Question 5 (16 marks) – Thermal equilibrium and thermal expansion

(a) 0.30 kg of water at 90 C is mixed with 0.20 kg of water at 20 C. Assuming no heat loss, calculate the final temperature. (4 marks)

(b) The measured final temperature is usually slightly lower than the calculated value. Explain why. (3 marks)

(c) 2.0 L of water is warmed by 10 C. The coefficient of volume expansion of water is 2.1 x 10^-4 per C. Calculate the increase in volume in cm3. (3 marks)

(d) Explain why hot water pipes are fitted with expansion joints at intervals. (3 marks)

(e) Explain why a thermometer reading should be taken only after it has become steady. (3 marks)

Question 6 (17 marks) – Gas laws, energy efficiency and cost

(a) The air in a car tyre is at 290 K and 200 kPa. After a drive the air reaches 310 K with the volume unchanged. Calculate the new pressure. (4 marks)

(b) Convert 126000 J of energy into kWh. (1 kWh = 3.6 x 10^6 J) (3 marks)

(c) If electricity costs $1.20 per kWh, calculate the cost of that energy. (3 marks)

(d) A house loses 250 J of energy per second. After insulation is fitted the loss falls by 60%. Calculate the new rate of loss and state two benefits. (4 marks)

(e) Suggest two ways of reducing energy use in the home and explain the principle of each. (3 marks)

Answers and marking notes

Question 1 – The kinetic particle model and the three states of matter

(a) In a solid the particles are closely packed in an ordered pattern and only vibrate about fixed positions (one mark); in a liquid they are less closely packed and can slide past one another (one mark); in a gas they are far apart and move randomly at high speed (one mark). [3 marks]

(b) Heating gives the particles more energy (one mark); they vibrate with a larger amplitude so the average spacing increases (one mark); the overall volume therefore increases (one mark). [3 marks]

(c) Temperature is a measure of the average kinetic energy of the particles (one mark); the higher the temperature, the greater the average kinetic energy (one mark). [2 marks]

(d) Particles move randomly and keep colliding with the walls of the container (one mark); each collision exerts a force on the wall (one mark); the average effect of very many collisions is the pressure (one mark). [3 marks]

(e) The spaces between liquid particles are very small, so they can hardly be pushed closer (one mark); the spaces between gas particles are large and can be greatly reduced by pressure (one mark). [2 marks]

(f) Gas particles move at higher speeds (one mark); there is more empty space between gas particles so they can pass freely (one mark); the particles therefore mix faster in a gas (one mark). [3 marks]

Question 2 – Specific heat capacity and heating calculations

(a) Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius (one mark); for water it is 4200 J/(kg°C) (one mark); so 1 kg of water needs 4200 J to rise by 1 degree Celsius (one mark). [3 marks]

(b) Temperature rise = 80 – 20 = 60 C (one mark); energy = m c dT = 0.50 x 4200 x 60 (one mark); = 126000 J (one mark); = 126 kJ (one mark). [4 marks]

(c) Energy = power x time (one mark); time = 126000 / 1200 (one mark); = 105 s (one mark). [3 marks]

(d) Total energy = 1500 x 105 = 157500 J (one mark); efficiency = useful energy / total energy (one mark); = 126000 / 157500 (one mark); = 80% (one mark). [4 marks]

(e) Water has a greater specific heat capacity than land (one mark); it warms up less for the same energy input (one mark); the sea breeze carries cooler air onshore, so daytime coastal temperatures are lower (one mark). [3 marks]

Question 3 – Melting, latent heat and cooling curves

(a) The energy supplied is used to break the bonds between the particles (one mark); the particles change from a regular arrangement to one that can slide (one mark); the energy becomes latent heat rather than kinetic energy, so the temperature does not change (one mark). [3 marks]

(b) Energy = m x L (one mark); = 0.20 x 334000 (one mark); = 66800 J (two marks). [4 marks]

(c) Time = energy / power (one mark); = 66800 / 1200 (one mark); = 55.7 s (one mark). [3 marks]

(d) Melting ice absorbs latent heat of fusion (one mark); the energy comes from the skin, so the skin cools (one mark); the melted water can then absorb more energy as it warms up (one mark); the total energy absorbed is therefore greater and the cooling effect is stronger (one mark). [4 marks]

(e) The temperature rises to 0 C and the first flat section is the melting of ice (one mark); it then rises to 100 C and the second flat section is the boiling of water (one mark); a flat section shows that the temperature stays constant during a change of state (one mark). [3 marks]

Question 4 – Conduction, convection and radiation

(a) Conduction transfers energy by vibrations of particles and occurs mainly in solids (one mark); convection relies on the bulk flow of a fluid and needs a liquid or a gas (one mark); radiation travels as electromagnetic waves and needs no medium, so it can cross a vacuum (one mark). [3 marks]

(b) Substitute: 0.50 x 0.020 x 20 / 0.010 (two marks); = 20 W (two marks). [4 marks]

(c) The sealed gap between the two panes contains air (one mark); air is a poor conductor of heat so conduction is slow (one mark); the sealed gap prevents bulk air movement and so suppresses convection (one mark). [3 marks]

(d) Water at the bottom is heated, expands and becomes less dense (one mark); the warmer water rises and cooler water sinks to replace it (one mark); this circulation carries energy through the kettle (one mark); convection needs gravity, so it does not occur naturally in a weightless environment (one mark). [4 marks]

(e) Dark surfaces absorb more of the incident radiation and reflect less (one mark); the absorbed radiation becomes internal energy and the surface warms up (one mark); one application is painting the absorber plate of a solar water heater black to absorb more energy (one mark). [3 marks]

Question 5 – Thermal equilibrium and thermal expansion

(a) Energy lost = energy gained (one mark); m1 (T1 – T) = m2 (T – T2) (one mark); 0.30 x (90 – T) = 0.20 x (T – 20) (one mark); solving gives T = 62.0 C (one mark). [4 marks]

(b) Some energy is lost to the surrounding air and to the container (one mark); the container itself absorbs some energy (one mark); the water therefore gains less energy and its final temperature is lower (one mark). [3 marks]

(c) dV = V beta dT (one mark); = 2.0 x 2.1 x 10^-4 x 10 = 4.2 x 10^-3 L (one mark); = 4.2 cm3 (one mark). [3 marks]

(d) Metal pipes expand when heated (one mark); if the pipe is rigidly fixed the expansion creates large stresses that can bend or crack it (one mark); expansion joints absorb the change in length and prevent damage (one mark). [3 marks]

(e) The thermometer needs time to reach thermal equilibrium with the object (one mark); before equilibrium the reading is still changing (one mark); a steady reading shows that both are at the same temperature, so the measurement is accurate (one mark). [3 marks]

Question 6 – Gas laws, energy efficiency and cost

(a) At constant volume pressure is proportional to absolute temperature (one mark); p2 = p1 x T2 / T1 (one mark); = 200 x 310 / 290 (one mark); = 213.8 kPa (one mark). [4 marks]

(b) kWh = 126000 / 3.6 x 10^6 (two marks); = 0.035 kWh (one mark). [3 marks]

(c) Cost = energy x unit price (one mark); = 0.035 x 1.20 (one mark); = $0.042 (one mark). [3 marks]

(d) New loss = 250 x (1 – 0.60) (two marks); = 100 J/s (one mark); benefits: less heating is needed so money is saved, and less fuel is burnt so carbon emissions fall (one mark). [4 marks]

(e) Use LED lamps, which convert more of the electrical energy into light rather than heat and are more efficient (one mark); add thicker loft insulation, which reduces heat loss by conduction and convection (one mark); both reduce the energy input needed (one mark). [3 marks]

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