Power – Definition and Unit of Power | Unit of Work
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Power – Definition and Unit of Power
In our daily life, we say that we work a lot. Whenever we feel some kind of exertion, being physical or mental or sometimes for various other activities like writing, playing, speaking, etc. we say that we are doing work. Herein, we will be elaborately studying about Power and the unit of Power that we use in everyday science.
In addition, a body which is capable of doing work contains energy because it requires energy to perform any sort of work. But, we all don’t work at the same rate.
Moreover, some do an amount of work in a very quick time, whereas the other takes more time. Furthermore, it is the rate of work which varies and the rate of doing work is Power.
Definition of Power
Power is the rate of doing work. It is not only important to know how much work a body has done but also the rate at which this is done by the body. For example, we say a person is physically fit if he/she not only climbs the floor of a building but also if he/she climbs it fast. Hence, power is defined as the time taken or the rate at which the work is done or the energy is transferred.
Measurement of Power
The Power measures the amount of work done by the body per unit of time and it is numerically equal to the work done by the body in one second.
If a body does a Work (W) in Time (T), then Power (P) is defined as, Power (P) = [Math Processing Error]
In terms of Force, we can define the Power as:
If a constant force F acts on a body and it moves or displaces the body by a distance S (in the same direction that of the applied force) in time T, then
the work done, W = F × S and
Power, P = [Math Processing Error]
Power, P = [Math Processing Error] = F×v,
since [Math Processing Error] = v (velocity or average speed).
Hence, Power = Force × Average Speed
The power of a body depends on the below two factors:
- The amount of work done by the body and
- Moreover, it is the time taken by the body to complete the work
If a body (or a machine) does work at a faster rate, then more power is spent by the body to complete the work.
Units of Power – SI, CGS, and MKS
Power is a scalar quantity.
The S.I. unit of Power is Watt (W).
In other terms, we spent one Watt of Power while completing one Joule of Work in one second.
1 Watt = 1 Joule / 1 second.
Other units of Power are Kilowatt (kW), Megawatt (MW) and Gigawatt (GW).
The relation between units of Power:
1 kW = 1000W, 1 MW = 1000000W and 1GW = 1000000000W
In MKS system the unit of power is [Math Processing Error]
In CGS system, the unit of power is erg per second.
Difference between Work and Power:
Work:
- Work done by a force is equal to the product of force and displacement (in the direction of the force).
- The work done by a body is independent of time.
- Joule (J) is the S.I unit of work.
Power:
- It is the rate of doing work of the body.
- Also, it depends on the time at which we do the work.
- The S.I. unit of Power is Watt (W)
Difference between Energy and Power:
Energy:
- The capacity of a body to do work is its energy.
- Furthermore, the energy of a body is independent of time
- Joule (J) is the S.I unit of energy.
Power:
- It is the amount of energy that the body spent in one second.
- It depends on the time at which we spent energy.
- The S.I. unit of Power is Watt (W).
Solved Question for You
Q: What is Horse Power?
Ans: Horse Power (HP) is another unit of Power, which is largely in use in mechanical engineering. It is useful in describing the output of automobiles, motorbikes, aeroplanes, etc.
1 Horse Power = 746 Watt or 0.746 kW