A tube light of 40W is used for 5h per day. Calculate the 'units' of energy consumed in one day by the tube light.

Energy  is defined as the ability to do work.

Power is defined as the rate at which energy is used or transmitted; it is equal to the amount of energy divided by the time it takes to use the energy. Its unit is the watt, which is one joule of energy used per second.

Power of electric bulb = 40W

                                        =0.04 kW

Time used, t = 5h

Energy = $\mathrm{Power} \times \mathrm{Time} \mathrm{taken}$

             $=0.04 kW \times 5 \mathrm{h}$

             $=0.2 kWh$

             $=0.2\left(units\right)$

The energy consumed by the tube light is 0.2 'units'.