We can get the unit of power by dividing the unit of work with that of time. Since the unit of work is joule (J) and the unit of time is second (s), the unit of power will be Joule/second (J/s). It is called Watt. Watt is denoted by W.

If one joule work is done in one second or the rate of transformation of energy is called one watt **1W= 1J / 1S = 1 Js ^{-1}**

Since watt is very smaller, its thousand times larger unit kilo-watt is used.

**1 kilo-watt = 1000 watt**

You have probably heard the word “Horse Power”. This unit of power was used earlier. Still today this unit is sometimes used to mean the power of a motor or a car.

**1 Horse Power = 746 watt**

Have you heard the word “kilowatt-hour”? What does it mean? Actually it is the unit of work or energy. We usually pay the bill of electricity of houses, factories etc measured in this unit. One kilowatt-hour means the energy that a machine with a power of one kilowatt uses in one hour. 60 watt mark on a bulb means that it transforms 60 Joules electrical energy to light and heat energy in one second.

200 megawatt power of an electrical power station means that it supplies 200000000 joules energy in one second. We are using this energy in houses, factories and offices.