Question

Establish the relation between the commercial unit and the SI unit of energy.

Answer 1

1. Energy is the capacity of doing work. Any object having the capability to do work is said to possess energy.
2. An object which possesses energy can exert a force and can transfer energy to another object and work is done.
3. Since energy is the capacity to do work it means its unit will be the same as that of work.
4. Hence SI unit of energy will be joule.
5. 1 joule of energy can be defined as the energy required to do one joule of work.
6. Since SI unit of energy (joule) is too small to use for large energy consumption therefore we use kWh.
7. 1kWh is the amount of energy consumed when a machine or appliance of 1kilowatt is operated for one hour.

Relation between kWh and joule-
$$\begin{gathered} 1kWh=1000Wh(\sin ce1kiloW=1000W) \\ also1hour=3600second \\ \Rightarrow 1kWh=\left(1000W\right)\times \left(3600second\right) \\ Hence1kWh=3.6\times {10}^{6}J \end{gathered}$$