A kettle is used to heat water. Describe the energy changes that take place from when the kettle is switched on until the water reaches its maximum temperature. Include reference to useful energy and waste energy in your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Electrical energy from the mains is transferred to the heating element of the kettle and then to the water as thermal energy.
The useful energy is the thermal energy that raises the temperature of the water.
Some of the energy is wasted – for example as heat lost to the surroundings, as sound and as heat in the kettle’s metal.
The total energy supplied by the mains equals the useful energy that heats the water plus the waste energy, in accordance with the conservation of energy.
The useful energy is the thermal energy that raises the temperature of the water.
Some of the energy is wasted – for example as heat lost to the surroundings, as sound and as heat in the kettle’s metal.
The total energy supplied by the mains equals the useful energy that heats the water plus the waste energy, in accordance with the conservation of energy.
Examiner tips
- Use the word "electrical energy" and "thermal energy" – the key terms. Show the energy flow: mains → kettle → water. Mention both useful and waste energy. State the conservation of energy principle to link the two.
- common_mistakes
- :
- Confusing the energy source with the energy stored. Omitting the waste energy or the conservation of energy statement. Using vague terms like "heat" without specifying useful vs waste.
Mark scheme (4 marks)
- Electrical energy is transferred to thermal energy (in the water / heating element)
- The useful energy transfer is the thermal energy that raises the temperature of the water
- Some energy is wasted / dissipated (e.g. as thermal energy lost to the surroundings / sound)
- The total energy input equals the useful energy output plus the waste energy (conservation of energy / energy cannot be created or destroyed)
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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