Electric Energy

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

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:

1. What is electric energy?
2. What is 1 joule?
3. What is commercial unit of energy?
4. Define 1 kilowatt hour.
5. What is the relationship between kilowatt hour and joule?