1. 1
   A student tests an old electric kettle. Each time the kettle is switched on, it is supplied with 240 000 J of electrical energy, of which 180 000 J is transferred usefully to heat the water. The rest is wasted, mostly heating the surrounding air and the kettle's casing.

   (a)

   What is the efficiency of the kettle?

   [1 mark]

   • A0.25
   • B1.33
   • C0.75
   • D0.60

   (b)

   Which single change to the kettle would be most likely to increase its efficiency?

   [1 mark]

   • AIncreasing the total electrical energy supplied to the kettle
   • BFitting better thermal insulation around the heating element and casing
   • CBoiling a larger volume of water each time
   • DUsing a longer power cable to connect the kettle to the socket

   (c)

   The manufacturer replaces the kettle's casing with a design that has better thermal insulation. State what happens to the energy wasted per use, and explain in terms of energy dissipation why this change improves efficiency.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A remote village currently relies entirely on a diesel generator (a non-renewable fossil fuel source) for its electricity. Engineers are considering adding a wind turbine and a small hydroelectric scheme fed by a nearby river to supply some of the village's electricity instead.

   (a)

   Which of the following is a renewable energy resource being considered for the village?

   [1 mark]

   • ADiesel
   • BNatural gas
   • CCoal
   • DHydroelectricity

   (b)

   Which statement correctly compares the wind turbine and the diesel generator as energy resources for the village?

   [1 mark]

   • AThe wind turbine produces a constant, reliable output at all times, unlike the diesel generator
   • BThe wind turbine will never run out, but its output depends on weather conditions, whereas the diesel generator gives a reliable output whenever fuel is available
   • CThe diesel generator is a renewable resource because it can be refuelled repeatedly
   • DThe wind turbine will eventually run out of fuel, unlike the diesel generator

   (c)

   Describe one advantage and one disadvantage of the village switching from the diesel generator to a combination of wind and hydroelectric power.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A factory uses an old electric motor to lift components. The motor is supplied with 5000 J of electrical energy for each lift and transfers 3000 J usefully to gravitational potential energy of the component. The rest is wasted as heat in the motor's coils and bearings due to friction.

   (a)

   Calculate the efficiency of the motor. Give your answer as a decimal.

   [3 marks]

   (b)

   The factory engineer suggests two possible changes: (1) regularly lubricating the motor's bearings, and (2) fitting thicker thermal insulation around the motor casing. Explain how each change could increase the efficiency of the motor, and suggest which change is likely to have the greater effect on the energy wasted as heat due to friction.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A national energy report shows that, over the last twenty years, the proportion of the country's electricity generated from coal has fallen sharply, while the proportion generated from wind and solar power has risen steadily. Nuclear power's contribution has stayed roughly constant, and natural gas use has fallen only slightly and remains significant, partly because it is used to fill gaps when wind and solar output are low. The government must now decide whether to approve a new gas-fired power station or a new hydroelectric dam to provide additional generating capacity for the next 40 years.

   (a)

   Using your knowledge of energy resources, explain the trends described in the report. Your answer should refer to the properties of the energy resources involved, including their availability, reliability and environmental impact.

   [6 marks]

   (b)

   Evaluate the government's choice between building a new gas-fired power station or a new hydroelectric dam, in terms of energy resource type, reliability, environmental impact, and long-term running costs, and recommend which option should be chosen, justifying your answer.

   [6 marks]

   Total for question 4: 12 marks

End of questions