A kettle is used to heat water. Explain what happens to the energy stored in the electrical supply during this process, including reference to any useful energy transfer and waste energy transfer that occurs.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student notices that the outside of a kettle feels warm to the touch after it has finished boiling. She also hears a rumbling sound as the water heats up.
Model answer (4 marks)
Electrical energy supplied to the kettle is converted into heat energy. The heat produced raises the temperature of the water – this is the useful energy transfer. Some of the heat also flows through the kettle’s walls into the surrounding air – this is waste energy transfer. In addition, a small amount of energy is released as sound (the rumbling noise) – another waste energy transfer. The total electrical energy supplied equals the sum of the useful energy in the water and all the waste energy transferred to the surroundings, in accordance with the conservation of energy.
Examiner tips
- Use the word ‘converted’ to show energy change; mention heat, sound and heat loss to surroundings; state conservation of energy at the end.
- Keep answer concise – 4 marks, so one sentence per point.
- Use UK spelling (e.g., ‘conservation’).
Common mistakes
- Failing to mention the heat loss through the kettle’s walls; treating sound as a useful transfer; not linking the total energy to the conservation of energy principle.
Mark scheme (4 marks)
- Electrical energy is transferred to thermal energy in the water (useful energy transfer).
- Energy is also transferred to the surroundings as heat through the kettle's walls (waste energy transfer).
- Energy is also transferred as sound (waste energy transfer), e.g. the rumbling noise heard during boiling.
- The total energy input equals the sum of all useful and waste energy transfers, in accordance with the conservation of energy.
Key terms in this question
useful energy transfer · waste energy transfer
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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