A swimming pool uses an electric pump to circulate water through a heating system. The pump transfers electrical energy, but not all of this energy is used to move the water. Some energy is dissipated as heat in the pump's motor and some is lost as sound. Explain how the efficiency of the pump could be improved, and describe what is meant by efficiency in this context.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A leisure centre manager notices that the pool pump becomes very warm during operation and makes a noticeable humming sound. She wants to improve the system so that more of the electrical energy input is used to move the water rather than being wasted.
Model answer (4 marks)
Efficiency is the ratio of useful output energy transfer to total energy input.
To improve the pump’s efficiency the manager could:
1. Lubricate the moving parts, which reduces friction and therefore less heat is lost.
2. Reduce the current drawn by the motor, which cuts the I²R losses in the motor windings and the wiring.
3. Minimise waste energy such as heat and sound – for example by using better insulation or a quieter motor – so that more of the electrical energy becomes useful work moving the water.
In this context efficiency means how much of the electrical energy supplied to the pump is actually used to move the water, compared with how much is lost as heat or sound.
To improve the pump’s efficiency the manager could:
1. Lubricate the moving parts, which reduces friction and therefore less heat is lost.
2. Reduce the current drawn by the motor, which cuts the I²R losses in the motor windings and the wiring.
3. Minimise waste energy such as heat and sound – for example by using better insulation or a quieter motor – so that more of the electrical energy becomes useful work moving the water.
In this context efficiency means how much of the electrical energy supplied to the pump is actually used to move the water, compared with how much is lost as heat or sound.
Examiner tips
- Define efficiency as a ratio of useful output to total input.
- Show specific actions that reduce friction, electrical losses and waste energy.
- Use the exact wording from the mark scheme.
- Keep each point short and to the point.
Common mistakes
- Confusing efficiency with power or energy.
- Failing to mention that heat and sound are forms of waste energy.
- Using vague terms like "improve" without explaining how.
Mark scheme (4 marks)
- Efficiency is the ratio of useful output energy transfer to total energy input
- Lubrication of moving parts in the pump reduces friction, which reduces heat loss / waste energy transfer
- Reducing the current through the motor decreases energy lost as heat in the wires / motor
- Recycling or reducing waste energy transfer (heat/sound) means more of the input energy becomes useful output, increasing efficiency
Key terms in this question
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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