Electrical Power and Energy Transfer

This lesson covers electrical power and energy transfer in circuits, including the key equations you need for the AQA GCSE Physics exam (4.2.3). These equations are essential for calculation questions and for understanding how energy is transferred in domestic and industrial contexts.

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What Is Electrical Power?

Power is the rate of energy transfer — it tells you how much energy is transferred per second.

Power is measured in watts (W).

1 watt = 1 joule per second (1 W = 1 J/s)

Larger powers are often measured in kilowatts (kW): 1 kW = 1000 W.

A 100 W light bulb transfers 100 joules of energy every second. A 2000 W kettle transfers 2000 joules of energy every second.

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Key Equations for Electrical Power

There are three important power equations you must know for the GCSE exam:

Equation 1: Power, Energy and Time

P = E / t

Or rearranged: E = P x t

Where:

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

Equation 2: Power, Current and Potential Difference