Subsection 10.6.13 Third Law of Thermodynamics
From now we may have known that the entropy difference between two points like the potential energy. Where we must define the base line to calculate the potential energy. We already have a natural base line thermodynamically, a system at absolute zero has zero entropy. This is sometimes called the third law of thermodynamics. The efficiency of Carnot engine,
\begin{equation*}
\eta= 1-\frac{T_{c}}{T_{h}}
\end{equation*}
If \(T_{c} =0,\) \(\eta =1,\) i.e., \(100\% \)efficient. It means if the temperature of the sink be zero, then complete conversion of heat into work is possible. But further lowering of temperature if it is already sufficiently low is not easy. Hence, third law states that it is impossible by any procedure to reduce temperature of any system to absolute zero.
