**Definition**

“** Power is defined as the rate of doing work or the rate of transfer of energy.**“

If an agent does a work W in time t, then power is given by:

Power = work/time or P =w / t

The S I unit of power is J s^{–1} = kg m^{2}s^{-3} = **watt **(W) [in honour of James Watt (1736 – 1819)] having the symbol W.

The C G S unit of Power is erg / s = g cm^{2}s^{-3}

**Define Watt**.

1 watt is the power of an agent, which 1 J work is done in one second.

1 watt = 1 joule /1 second or 1 W = 1 J s^{–1}

We can also say that power is 1 W when the rate of consumption of energy is 1 J s^{–1}

.We express larger rates of energy transfer in kilowatts (k W).

1 kilowatt = 1000 watts

1 kW = 1000 W

1 kW = 1000 J s^{–1}

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The power of an agent may vary with time.

This means that the agent may be doing work at different rates at different intervals of time.

Therefore the concept of average power is useful. We obtain average power by dividing the total energy consumed by the total time taken.