The efficiency of Carnot engine is,

η = 1 –

Where T1 is the temperature of the source and T 2 that of sink.

Since, So, η = 1 –

To obtain 100% efficiency (i.e., η = 1), Q 2 must be zero that is, 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 2nd law of thermodynamics. Hence, a negative temperature

on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.