A boiler containing water is plugged into a 230 V mains supply. The heater in the boiler is operating at full power.

1. (a)(i)The power used by the heater is 2.8kW. Calculate the current in the heater.[3]
2. (a)(ii)The wiring in the cable from the socket and in the boiler remains safe and does not overheat provided that the current is less than 20A. Suggest a suitable fuse rating for the circuit.[1]
3. (b)(i)The specific heat capacity of water is 4200J/(kg°C). The heater is used to increase the temperature of 6.3 kg of water. In a certain time, the temperature of the water increases from 23°C to 49°C. Calculate the change in the internal energy of the water.[2]
4. (b)(ii)The heater supplies thermal energy to the water at a constant rate. It takes more time for the temperature of the water to increase from 49°C to 75°C than from 23°C to 49°C. In both cases, the increase in temperature is the same. Suggest why it takes more time for the temperature to increase from 49°C to 75°C.[1]
5. (c)(i)[Figure 10.1] shows the heater at the bottom of the water in the boiler. Explain how thermal energy is transferred from the heater throughout the water.[3]
6. (c)(ii)The part of the boiler that holds the water is made from steel. Describe, in terms of particles, how thermal energy passes through the steel.[3]
7. (c)(iii)State and explain, in terms of particles, what happens to the density of the steel as its temperature increases.[2]

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