We can define power as the rate of doing work, it is the work done in unit time.
Power
The SI unit of power is Watt (W) which is joules per second (J/s). Sometimes the power of motor vehicles and other machines is given in terms of Horsepower (hp), which is approximately equal to 745.7 watts.
We can define average power as the total energy consumed divided by the total time taken. In simple language, we can say that average power is the average amount of work done or energy converted per unit of time.
Power Formula
Power is defined as the rate at which work is done upon an object. Power is a timebased quantity. Which is related to how fast a job is done. The formula for power is mentioned below.
Power = Work / time
P = W / t
Unit of Power
The unit for standard metric work is the Joule and the standard metric unit for time is the second, so the standard metric unit for power is a Joule / second, defined as a Watt and abbreviated W.
Q1. A 60watt bulb is switched on 24 hours a day and there is another 60watt bulb that is turned on for only 12 hours. Find the energy consumed by both the bulbs in one day.
Solution:
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 kWh (kilowatthour)
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 = Total energy consumed / Total time taken
Therefore, the average power for our light bulbs will be,
= (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 (kilowatthour), which stands for 1 kilowatt of power is been consumed every 1 hour, where kWh is the unit of energy.
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