A household uses several electrical appliances every day. Explain why the kilowatt-hour is used to measure domestic energy consumption rather than the joule.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Electricity suppliers charge customers based on the amount of energy they use at home. The unit shown on a household energy bill is the kilowatt-hour (kWh).
Model answer (4 marks)
The joule is a very small unit of energy, so the numbers for household consumption would be huge and difficult to read.
The kilowatt‑hour (kWh) gives more manageable, convenient numbers for domestic use.
A kWh is defined as the energy used by a one‑kilowatt appliance running for one hour, so it relates directly to the power rating and time.
This makes it straightforward to calculate the cost of running appliances and to compare the energy use of different appliances at home.
The kilowatt‑hour (kWh) gives more manageable, convenient numbers for domestic use.
A kWh is defined as the energy used by a one‑kilowatt appliance running for one hour, so it relates directly to the power rating and time.
This makes it straightforward to calculate the cost of running appliances and to compare the energy use of different appliances at home.
Examiner tips
- Use the word ‘kilowatt‑hour’ and explain its definition; link it to power and time.
- Show why the joule is impractically small for household figures.
- Mention cost calculation and comparison of appliances.
Common mistakes
- Confusing joule with watt‑hour or kilojoule.
- Failing to explain the definition of a kWh.
- Using vague terms like ‘big’ or ‘small’ without justification.
Mark scheme (4 marks)
- The joule is a very small unit of energy
- The kilowatt-hour gives more manageable / convenient numbers for domestic use
- The kilowatt-hour is defined as the energy used by a one-kilowatt appliance running for one hour / it relates directly to power-rating and time
- This makes it straightforward to calculate the cost of running appliances / to compare energy use of different appliances at home
Key terms in this question
kilowatt-hour · domestic energy consumption
Related
- All Eduqas GCSE Physics revision notes →
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- Decode the mark scheme abbreviations →
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