# What is the unit of Work or Energy?

There are various type of units of energy as we used in various case. In this topic I am going to discuss about the various units of energy. So at first I recommend you to have a quick look at Work Power Energy topics so that if you do not know what is work and power, you can understand those.

The S.I unit of energy is Joule (J) and C.G.S unit of energy is erg.

1 J = 107 erg.

The higher units of energy are :

Watt hour (Wh) and Kilowatt hour (KWh) :

Watt hour (Wh) : 1 watt hour is the energy spent (or work done) by a source of power 1 Watt in 1 hour. I,e.,

1 watt hour = 1 watt × 1 hour

= 1  J / Sec × 3600 sec

= 3600 Joul = 3.6 kJ

Kilowatt hour : One kilowatt hour (1 kWh) is the energy spent (or work done) by a source of power 1kW in 1 hour. i.e,

1 kilowatt hour (kWh) = 1 kilowatt × 1 hour

= 1000 Joul/sec × 3600 sec

= 3.6 × 106 Joul = 3.6 Mega Joule.

Note: Watt (W) and kilowatt (kW) are the units of power, while Watt-hour (Wh) and kilowatt-hour (kWh) are the units of work or energy since power × time = work or energy.

Calorie : heat energy is usually measured in Calorie. 1 calorie is the heat energy required in rising the temperature of 1 g of water from 14.5°C to 15.5°C (or through 1°C). It is related to joule as

1 J = 0.24 calorie or 1 calorie = 4.2 Joule

Kilocalorie is the bigger unit of heat energy.

1 Kilocalorie = 100 calorie = 4200 Joule.

Electron volt : The energy of the atomic particles is very small, so it is measured in electron volt (eV).

1 eV is the energy gained by an electron when it is accelerated through a potential difference of 1 volt. i.e.,

1 eV = Charge on an electron × 1 volt

= 1.6 × 10-19 coulomb  × 1 volt

= 1.6 × 10-19 Joule.

`1 eV = 1.6 × 10-19 Joule.`