A large test-tube contains a thermometer and some solid wax at a temperature of 21 °C. At time t = 0, the test-tube is partially immersed in a beaker of boiling water and the temperature of the wax is recorded for the next 600 s. Fig. 4.1 shows the variation of the temperature of the wax with time t. [Figure 4.1]

1. (a)Explain how Fig. 4.1 shows that the melting temperature of the wax is 63 °C.[1]
2. (b)(i)As the temperature of the wax increases, the energy in the internal energy store increases. The mass of the wax in the test-tube is 0.040 kg and its temperature at time t = 0 is 21°C. The specific heat capacity of wax is 2100J/(kg°C). Using Fig. 4.1, determine the increase in the energy in the internal energy store of the wax between t = 0 and t = 220 s. Show your working.[3]
3. (b)(ii)Describe what happens to the motion of the molecules of the solid wax as the internal energy of the wax increases.[2]
4. (c)When the wax reaches its melting temperature, energy continues to be transferred thermally to the wax. Describe, in terms of the forces between particles, why energy is required to melt the wax.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.