# Electrical energy

## Electrical energy

• The SI unit of electrical work done for electrical energy expanded in a circuit is also joule exactly the same  as for mechanical energy. It is defined as under :
One joule of energy is expended electrically when one coulomb is moved through a potential              difference (p.d.) of 1 volt.

• ‌Suppose a charge of Q coulombs moves through a potential difference of V volts . Then electrical energy expended is given  by ;

Electrical energy expended = VQ joules
= VIt joules
= I^2  Rt joules

Here (Q = It)
(V = IR)
• It may be mentioned here that joule is also known as watt - second .  i.e. 1 joule = 1 Watt - sec.
• When we are dealing with large amount of electrical energy, it is often convenient to express it in kilowatt hours (Kwh).

1kwh = 1000 watt - hours = 1000 × 3600 watt -  sec or joules
1kwh = 36 ×1000000 joules or watt-sec.

• Although practical unit of electrical energy is kwh, yet it is easy to see that this unit is readily converitable to joules with the help of above relation.