Power is defined as the rate of doing work, it is the work done in unit time, and the SI unit is given as watt (W) which is joules per second (J/s) sometimes power of motor vehicles and other machines are given in terms of Horsepower (hp) which is approximately equal to 745.7 watts.

Power is always dependent on work done, so if a person does work at different rates his power also differs at different times, this is where the concept of average-power comes into picture. Average-power is defined as the total energy consumed divided by the total time taken, now let us consider an example,

A 60 watt bulb is switched ON 24 hours a day and there is another 60 watt bulb which is turned ON for only 12 hours. Now let’s look at the energy consumed by both the bulbs in one day.

For the first 12 hours both bulb A and B are turned ON therefore,

Power = 60 + 60 = 120 watts

Energy = Power x Time

= 120 x 12 = 1.44 kW h (kilo watt hour)

Now for the next 12 hours only bulb A would remain ON hence,

Power = 60 watts

Energy = 60 x 12 = 0.72 kW h

In this scenario the power consumed during the whole day varies as one bulb is turned ON for only 12 hours so we have to calculate average power,

Average Power = \( \frac {Total~energy~consumed}{Total~time~taken} \)

Therefore the average power for our lightbulbs will be,

\( \frac {1.44~+~0.72}{24} \)

= 0.092 kW

You must have noticed that electrical components and energy meters in homes use a unit called kWh (kilowatt hour), which stands for 1 kilowatt of power is been consumed every 1 hour, kWh is the unit of energy.

Refer to our energy and work articles to understand them in details, the following points about power will summarise this topic:

- (a) It is the rate at which energy is been used.
- (b) It decides how quickly work could be done.
- (c) It could change so there are two ways to measure power.
- Instantaneous: The power at any given moment of time.
- Average: The total energy used divided by total time, it’s the average of all the instantaneous powers.

Learn more about energy and work by subscribing BYJUs on Youtube.