The electric energy consumed by an electrical appliance is given by the product of its power and the time for which it is used i.e.
Electrical energy = Power X time
or, E = P X t
The S.I. unit of electrical energy is 1 joule
One joule is the amount of electrical energy consumed when an electrical appliance of 1 watt power is used for one second, i.e.
1 Joule = 1 watt X 1 second
or 1 J = 1 w X 1 s
or 1 J = 1ws
Commercial Unit of Energy: - Kilowatt Hour
One kilowatt hour is the total electrical energy consumed when an electrical appliance having a power of 1 Kilowatt is used for 1 hour. It is written as kWh in short form.
Relationship between Kilowatt Hour and joule
1 kWh = 1 kilowatt X 1 hour
so 1 kWh = (1000w) X (60 X 60 sec.)
= 3600000 watt seconds
or 1 kWh = 3.6 X 106 J
Test Your Understanding and Answer These Questions:
- What is electric energy?
- What is 1 joule?
- What is commercial unit of energy?
- Define 1 kilowatt hour.
- What is the relationship between kilowatt hour and joule?
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