where, \(T_{1}\) is the temperature of the source and \(T_{2}\) that

of sink. since, \(\frac{T_{2}}{T_{1}}=\frac{Q_{2}}{Q_{1}}\)

So, \(\quad \eta=1-\frac{Q_{2}}{Q_{1}} |\)

To obtain \(100 \%\) efficiency (i.e., \(\eta=1), Q_{2}\) must be zero i.e., if a sink at absolute zero would be available, all the heat taken from the source would have been converted into work. The temperature of sink means a negative temperature on the absolute scale at which the efficiency of engine is greater than unity. This would be a violation of the \(2\, nd\) law of thermodynamics. Hence, a negative temperature on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.