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# Power as work done over time taken

Power $(P)$ is the energy generated per unit time.

Because energy is the ability to do work, power can also be defined as the work done per unit time.

A motor which uses a high power can do more work (or use more energy) in a fixed amount of time than a motor with a low power.

The power is given by: $$\Tblue{\text{power}}=\frac{\Tred{\text{work done}}}{\Torange{\text{time taken}}}=\frac{\Tred{\text{energy generated}}}{\Torange{\text{time taken}}}$$

The SI unit of power is the watt $(\text{W})$. One watt is equivalent to one joule per second (i.e. $1\text{ W}=1\text{ J s}^{-1}$).

A light bulb that does $\Tred{500 \text{ J}}$ of work in $\Torange{5 \us}$ has a power of $\Tblue{100 \text{ W}}.$

A microwave with a power of $\Tblue{0.8 \text{ kW}}$ delivers $\Tred{16 \text{ kJ}}$ of energy during a $\Torange{20 \us}$ period.

Coal is burnt in this power station to create electrical power for homes.