Power and Efficiency

This lesson covers power — the rate of energy transfer — and efficiency — the proportion of energy that is usefully transferred. Both are fundamental concepts in the AQA GCSE Physics specification (Section 4.1) and are tested with both calculation and explanation questions.

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What Is Power?

Power is the rate at which energy is transferred or the rate at which work is done. It tells you how quickly a device converts energy from one form to another.

An appliance with a high power rating transfers energy quickly. An appliance with a low power rating transfers energy slowly.

Power Equations

There are two key equations for power:

P = E / t

Where:

• P = power in watts (W)
• E = energy transferred in joules (J)
• t = time in seconds (s)

P = W / t

Where:

• W = work done in joules (J)

Quantity	Symbol	Unit
Power	P	watts (W)
Energy transferred	E	joules (J)
Work done	W	joules (J)
Time	t	seconds (s)