Solution:

Assume we have a machine that consumes 1000 J of energy per second. This machine will consume 1 kWh of energy if used continuously for one hour.

Thus, $1\mathrm{kW}$ h is the energy used in one hour at the rate of $1000J{s}^1$ (or $1\mathrm{kW}$ ).

$1kwh=1\mathrm{kw}\times 1\mathrm{kh}$

$=1000W\times 3600s$

$3600000J$

$1\mathrm{kwh}=3.6\times {10}^6\mathrm{J}$