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)

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.

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