From the equation of Efficiency of a heat engine

Efficiency (η) = q₂-q₁ / q₂ = T₂-T₁ / T₂

The efficiency of an engine working reversibly depends only on the temperature of the source and the sink and is independent of the nature of the substance or substance used or modes of operation of the engine. This can be put in the form of a statement known as CARNOT THEORM according to which:

The efficiency of a reversible heat engine depends only upon the temperature of the source and the sink and is independent of the nature of the working substance or substances used or mode of operation of the engine.

▪️The same idea may be expressed by stating that all the periodic machines working reversibly between the same temperature of source and sink have the same efficiency.

▪️It is also clear from the above discussion that while all the other form nof energy can be completely converted into heat , the complete conversion of heat into any other form of energy cannot occur witth out leaving some lasting changes some where in the system .

▪️ This help us to enunicate second law of thermodynamics according to which it is not possible to convert heat into work with out  compensation.