SI unit of Power | What is the SI unit of Power
- Watt
Force, energy, work are the commonly used terms in mechanical physics. Along with these terms the strength of mechanical objects also essential to study. So we define a term power which helps us to understand strength of any machine or object.
Power of object is defined as the amount of work done per unit time. Or
Rate of doing work is also called as power.
Then power is given as,
∴ power = work/time
∴ P = W/t
Where, W = work done ,t = time
From the above equation we can have unit of power as joule per second.
Sir James Watt, who discovered the first steam engine, which successfully used in train. To understand the mechanism of engines in modern era of automobile, steam engine invented by James Watt is found to be a milestone. This discovery leads the automobile industries to the new modern era.
Considering the efforts of Sir James Watt in the field of mechanical physics, international system of unit had decided to rename the unit of power as watt.
∴ P = W/t
Then , joule per second is equivalent to watt.
∴ joule/second is then renamed as watt.
Hence, SI unit of power is then taken as ‘watt’. Its symbol is ‘W’
∴ 1 joule/1 second = 1 watt
i.e. when 1 joule of work is done per second, the power is equal to 1 watt.
Generally, 1 watt power is very small in practice, so the power is written with some prefixes like,
1 kW= 103 W
1 MW= 106 W
Horsepower is also another unit of power, used to indicate strength of motors, water pumps etc.
1 horsepower = 746 watt
Important Faq on SI unit of Power
Q.1) How power of electric equipments is calculated?
Answer: Consider any electric equipment like refrigerator, which requires 220 V potential difference and 10 A current. Then according to formula, power of that refrigerator will be,
P = VI
P = 220 × 10
P = 2200 W
P = 2.2 kW
Q.2) How the consumption of electric energy spent is calculated by electricity board?
Answer: Suppose we used electric iron of power 500 W for 1 hour daily, then the electric energy consumed by an iron will be,
E = P. t
E = 0.5 kW × 1 hr.
E = 0.5 kWhr
So the energy consumed by iron will be 0.5 kWhr. If any electric equipment consumes energy of 1 kWhr, then electricity board charges us for 1 unit of energy. i.e. approximately Rs. 10 (as per new cost)
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