GCSE Physics · AQA 8463 · Topic 4.2.4
Energy transfers
Key points
- The power of a component: or (in watts).
- Energy transferred depends on power and time: , and on charge and p.d.: .
- Appliances transfer energy from the mains or batteries to useful stores, such as the kinetic energy of a motor or the thermal energy of a kettle.
- The power rating of an appliance tells you how much energy it transfers each second.
- The National Grid links power stations to consumers. Step-up transformers raise the p.d. to very high values so the current is low, which cuts energy losses by heating in the cables. Step-down transformers lower it for safe use in homes.
- For an ideal transformer, power in = power out, so .
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Electrical appliances exist to transfer energy: to a motor's kinetic store, a kettle's thermal store or a speaker's sound. This sub-topic shows how to calculate the power and energy involved, and why electricity is sent across the country…
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