A full set of ten original structured questions in the style of Paper 4, covering the whole of Temperature: thermal equilibrium, the thermodynamic scale, and specific heat and latent heat. Each question is linked to the lesson it draws on; attempt them all, then reveal the worked solutions.
Two metal blocks A and B are placed in thermal contact and isolated from their surroundings, as shown in Fig. 1.1. Block A starts at 85 °C and block B starts at 25 °C.
(a) State what is meant by thermal equilibrium between two bodies. [2]
(b) For the two blocks in contact:
(i) state the direction of the net transfer of thermal energy and explain your answer, [3]
(ii) state what is true of the two temperatures once thermal equilibrium is reached. [1]
(c) Using T / K = θ / °C + 273.15:
(i) express the starting temperature of block A in kelvin, [1]
(ii) a block later has a thermodynamic temperature of 300 K; state this in °C. [1]
(d) State the Celsius value of absolute zero, and state what is special about it in terms of the energy of the particles. [2]
(e) State one reason the thermodynamic temperature scale is preferred to a scale defined by the expansion of a particular liquid. [2]
A metal block of mass 0.80 kg is heated by a well-lagged electric heater of power 50 W, as shown in Fig. 2.1. In a time of 4.0 minutes the temperature of the block rises from 18 °C to 52 °C.
(a) Define the specific heat capacity of a substance. [2]
(b) Calculate the electrical energy supplied by the heater in this time. [2]
(c) Assuming all this energy is transferred to the block, calculate the specific heat capacity of the metal. [3]
(d) In practice some energy is lost to the surroundings. Explain why this makes the experimental value of the specific heat capacity larger than the true value. [2]
(e) Suggest one change to the procedure that would reduce this error. [1]
(f) The same quantity of energy from part (b) is supplied instead to 0.80 kg of water, of specific heat capacity 4200 J kg⁻¹ K⁻¹. Calculate the rise in temperature and comment on its size. [3]
This question is about changes of state. Specific heat capacity of ice = 2100 J kg⁻¹ K⁻¹, specific heat capacity of water = 4200 J kg⁻¹ K⁻¹, specific latent heat of fusion of ice = 3.3 × 10⁵ J kg⁻¹.
(a) Define the specific latent heat of fusion of a substance. [2]
(b) An electric heater of power 40 W melts 72 g of ice, already at 0 °C, in 5.0 minutes. Use this to calculate the specific latent heat of fusion of ice. [3]
(c) Explain why, while the ice is melting, energy is supplied yet the temperature does not change. [2]
(d) The specific latent heat of vaporisation of water is much greater than its specific latent heat of fusion. Suggest, in molecular terms, why this is so. [2]
(e) A mass of 0.050 kg of ice at −10 °C is heated until it becomes water at 20 °C (Fig. 3.1). Calculate the total energy required. [4]
Two blocks at different temperatures are placed in contact inside a thermally isolated container, as shown in Fig. 4.1.
(a) State what is meant by thermal equilibrium. [2]
(b) State the direction of the net flow of thermal energy before equilibrium. [1]
(c) Explain, in terms of energy, why the hot block cools while the cold block warms. [2]
(d) State the quantity that determines the direction of net thermal energy flow. [1]
(e) At equilibrium, state whether the two blocks are at the same temperature and whether they hold the same internal energy. [2]
(f) Explain why two objects with equal internal energies need not be at the same temperature. [2]
This question is about the thermodynamic (kelvin) temperature scale.
(a) State what is meant by absolute zero. [2]
(b) Write the relation between thermodynamic temperature T in kelvin and Celsius temperature θ. [1]
(c) Convert 27 °C to kelvin, and 200 K to degrees Celsius. [2]
(d) Explain why a temperature change of 1 °C is equal to a change of 1 K. [1]
(e) State what is meant by the thermodynamic scale being independent of the substance used. [2]
(f) The mean kinetic energy of gas molecules is proportional to T in kelvin. Explain why this relation would fail if θ in °C were used. [2]
Thermometers measure temperature through a physical property that varies with it.
(a) State two physical properties that can be used to measure temperature. [2]
(b) Explain what is meant by calibrating a thermometer using two fixed points. [2]
(c) Explain why two different thermometers may disagree at temperatures between the fixed points. [2]
(d) State one advantage of the thermodynamic scale over an empirical scale. [2]
(e) A resistance thermometer reads 100 Ω at 0 °C and 138 Ω at 100 °C. Assuming a linear response, find the temperature when its resistance is 119 Ω. [2]
A 2.0 kW electric heater warms 1.5 kg of water. The specific heat capacity of water is 4200 J kg⁻¹ K⁻¹.
(a) Define specific heat capacity. [2]
(b) Calculate the energy needed to raise the water from 20 °C to 100 °C. [2]
(c) Calculate the time this would take if no energy were lost. [2]
(d) In practice the heating takes longer. State and explain why. [2]
(e) Calculate the initial rate of rise of temperature of the water. [2]
(f) State one assumption made in part (e). [1]
A 0.80 kg metal block is heated by a 50 W heater for 4.0 minutes, and its temperature rises by 25 °C.
(a) Calculate the electrical energy supplied. [2]
(b) Assuming no energy is lost, calculate the specific heat capacity of the metal. [2]
(c) The accepted value is lower than this. State and explain why this method overestimates the specific heat capacity. [2]
(d) Suggest one improvement that would reduce this error. [1]
(e) Using the value from (b), calculate the initial rate of rise of temperature. [2]
(f) Explain why measuring the temperature rise over a short interval improves the accuracy. [2]
A 0.30 kg block of ice at 0 °C is heated until it becomes water at 40 °C. The specific latent heat of fusion of ice is 3.3 × 10⁵ J kg⁻¹ and the specific heat capacity of water is 4200 J kg⁻¹ K⁻¹. Fig. 9.1 shows how the temperature varies with energy supplied.
(a) Define the specific latent heat of fusion. [2]
(b) Calculate the energy needed to melt the ice. [2]
(c) Calculate the energy needed to warm the resulting water from 0 °C to 40 °C. [2]
(d) Calculate the total energy supplied. [1]
(e) Explain why the temperature stays constant while the ice melts, even though energy is supplied. [2]
(f) State why the specific latent heat of vaporisation is much larger than that of fusion. [2]
A 0.50 kg copper block at 200 °C is dropped into 0.40 kg of water at 20 °C in an insulated container. This question links thermal equilibrium with specific heat capacity. Take c(copper) = 390 J kg⁻¹ K⁻¹ and c(water) = 4200 J kg⁻¹ K⁻¹.
(a) State the principle used to find the final temperature. [2]
(b) Write the energy-balance equation for the block and the water. [2]
(c) Calculate the final equilibrium temperature. [3]
(d) State the assumption made in this calculation. [1]
(e) Explain, in terms of thermal equilibrium, why the block and water end at the same temperature. [2]
(f) State whether the block and the water hold equal internal energies at equilibrium. [1]
Mark this once you have attempted all ten questions and checked your working against the solutions. Revealing the solutions alone does not count.