The unit of work done of energy expended is joule. it is equal to the energy expended in passing 1 coulomb of charge through a resistance or 1 ohm i.e. the energy expended in passing one ampere current for 1 second through a resistances of one ohm is taken as one joule. It may also be expressed as 1 watt-see i.e. one watt of power consume for one second.

i.e. 1 joule = 1 watt-second

The unit of energy, joule or watt-sec is too small for practical purposes, so a bigger unit Mega joule (MJ) or kilowatt-hour (kwh) is used in electrical engineering

1 kwh = 1000 watt-hours= 1,000 x 3,600 watt-seconds or joules= 3.6 MJ

The kwh, also called the Board of Trade (B.O.T.) unit, is the energy absorbed by supplying a load of 1 kw or 1000 watts for the period of one hour, this is legal unit on which charges for electrical energy are made, and, therefore, it is called the Board of Trade (B.O.T.) unit.

Watt: It is defined as the power expended when there is an unvarying current of one ampere between two points having a potential difference of one volt. As already stated the bigger unit of power is kw or Mega watt.

1 kw = 1,000 watts
1 MW = 1,000 kw = 10⁶ watts

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