Topic 10 – Electricity and circuits — Edexcel GCSE Physics
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Topic 10 – Electricity and circuits explained
A domestic appliance transfers energy from the supply to other stores at a rate set by its power rating.
Read the full explanation
Power equals energy transferred per unit time, so energy transferred equals power multiplied by time. A 2000 W kettle switched on for 300 s transfers 2000 × 300 = 600 000 J, or 600 kJ, mostly to the thermal store of the water. A 10 W lamp left on for 10 hours (36 000 s) transfers 10 × 36 000 = 360 000 J, or 360 kJ, to the surroundings by heating and light. A higher power rating means a faster rate of energy transfer, so the same energy is delivered in less time. The change in stored energy of the appliance and its surroundings depends on both the power rating and how long it is used.
Your focus
- Describe the relationship between power rating and the rate of energy transfer.
- Calculate the energy transferred by an appliance from its power rating and time of use.
- Explain, with examples, how power rating and duration affect changes in stored energy.
Topic 10 – Electricity and circuits exam tips
Marking Points
- States that power is the rate of energy transfer, so energy transferred equals power multiplied by time.
- Calculates the energy transferred by a named appliance from its power rating and the time it is used.
- Explains that a higher power rating transfers energy at a faster rate, so the same energy is delivered in less time.
- Gives a worked example, such as a 2000 W kettle used for 300 s transferring 600 000 J.
- Explains that the change in stored energy depends on both the power rating and the duration of use.
- Identifies the stores that gain energy, such as the thermal store of water or the surroundings.
Examiner Tips
- 💡Show the equation and substitute values with units before giving the answer.
- 💡Convert time to seconds so the energy comes out in joules.
- 💡Use a clear example with numbers to show how power rating and time together set the energy transferred.
Common Mistakes
- Treats power rating as the total energy used; correct this by stating that power is a rate and energy depends on time as well.
- Uses time in minutes or hours without converting to seconds; correct this by converting to seconds before multiplying.
- Assumes a higher power rating always means more energy transferred; correct this by noting that a low-power appliance used for longer can transfer more energy.