A household appliance transfers electrical energy into useful and waste energy. Explain what is meant by useful energy transfer and waste energy transfer, and give one example of each for an electric hairdryer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Useful energy transfer is the transfer of energy by a system to directly serve the purpose of the system.
Example of useful energy transfer for a hairdryer: thermal energy from the heating element that dries the hair.
Waste energy transfer is the transfer of energy by a system to a form that does not directly serve the purpose of the system.
Example of waste energy transfer for a hairdryer: sound energy produced by the motor and fan, or heat lost to the surrounding air and the motor casing.
Example of useful energy transfer for a hairdryer: thermal energy from the heating element that dries the hair.
Waste energy transfer is the transfer of energy by a system to a form that does not directly serve the purpose of the system.
Example of waste energy transfer for a hairdryer: sound energy produced by the motor and fan, or heat lost to the surrounding air and the motor casing.
Examiner tips
- Use the exact definition of useful and waste energy transfer as given in the mark scheme.
- Give one clear example for each – thermal for useful, sound or unwanted heat for waste.
Common mistakes
- Confusing useful energy with waste energy, e.g. calling the heat that dries the hair waste.
- Giving an example that is not directly related to the hairdryer, such as the electricity supplied by the mains.
Mark scheme (4 marks)
- Useful energy transfer is the transfer of energy by a system to directly serve the purpose of the system
- Example of useful energy transfer for a hairdryer: thermal/heat energy (to dry/warm the hair) OR kinetic energy (from the fan/motor to move air)
- Waste energy transfer is the transfer of energy by a system to a form that does not directly serve the purpose of the system
- Example of waste energy transfer for a hairdryer: sound energy (noise from the motor/fan) OR unwanted thermal energy transferred to the surroundings / heating the motor casing
Key terms in this question
useful energy transfer · waste energy transfer
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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