Question

Does the entropy per cycle increase, decrease, or remain the same for (a) a Carnot engine, (b) a real engine, and (c) a perfect engine (which is, of course, impossible to build)?

Short answer

a) For the Carnot engine, the entropy per cycle remains the same.

b) For the real engine, the entropy per cycle increases.

c) For the perfect engine, the entropy per cycle decreases.

Step-by-step solution

The given data

a) A Carnot engine

b) A real engine

c) A perfect engine

Understanding the concept of entropy change

Entropy change is a phenomenon that quantifies how disorder or randomness has changed in a thermodynamic system. From the processes followed by the Carnot engine, real engine, and perfect engine, we can predict the entropy change.

(a) Calculation of the entropy change for a Carnot engine

The Carnot engine follows the reversible process. The entropy per cycle remains the same for the reversible engine.

Hence, entropy remains the same for a Carnot engine.

(b) Calculation of the entropy change for a real engine

A real engine loses energy due to the friction and heat loss. It follows an irreversible process. For reversible process,$\Delta S>0$

Therefore, entropy of the real engine increases per cycle.

(c) Calculation of the entropy change for a perfect engine

This is an imaginary engine in which energy extracted as heat from the high temperature reservoir is converted completely to work.

Therefore, entropy per cycle of a perfect engine decreases which violates the second law of thermodynamics.