GCSE Physics

The kilo-watt-hour (kWh)

The kilowatt-hour (kWh) is a unit of energy. But how much?

We have seen that: energy (kWh) = power (kW) × time (h)

Normally we want energy in joules (J) and time in seconds (s). The kW above is 1000 W (1000 J/s). The hour is 3,600 seconds, so:

1 kWh = 1,000 J/s × 3,600 s

1 kWh = 3,600,000 J

1 kWh = 3·6 MJ (mega joules: see prefixes)

The kWh is a large unit of energy used to measure how much energy is used in homes.

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