Thermal energy transferAQA A-Level Physics: Mind map

Exam questions on Thermal energy transfer

1. An electric kettle has a heating element of power 2.2 kW. It contains 2.0 kg of water at 20 °C, which is heated to 100 °C. The specific heat capacity of water is 4180 J kg⁻¹ K⁻¹.
   In practice the kettle takes longer than the time calculated in part (b). Suggest two reasons why.2 marks
2. A gas is trapped in a cylinder by a piston. The piston is pushed in quickly, so that 450 J of work is done on the gas, and during the process 120 J of energy is transferred from the gas to its surroundings by heating.
   Use the idea of internal energy to explain why the temperature of the gas rises when it is compressed quickly.2 marks
3. A beaker contains 0.250 kg of ice at 0 °C. It is heated by a 150 W immersion heater, and all of the energy from the heater is transferred to the ice. The specific latent heat of fusion of ice is 3.34 × 10⁵ J kg⁻¹.
   The temperature of the ice remains at 0 °C while it melts, even though energy is being supplied. Explain this in terms of the energies of the molecules.3 marks