Consider a cycle followed by an engine, (figure)

1 to 2 is isothermal 2 to 3 is adiabatic 3 to 1 is adiabatic
such a process does not exist because

Options

A. heat is completely converted to mechanical energy is completely converted to heat in this process, which is not possible.
B. mechanical energy is completely converted to heat in this process, which is not possible.
C. curves representing two adiabatic processes don’t' intersted.
D. curves representing an adiabatic process and an isothermal process don't intersect.

Answer

A, C

Explanation

(a) The given process is a cyclic process i.e., turns to the original state 1.
Hecne, change in internal energy dU=0
`rArrdQ=dU+dW=0+dW=dW`
Hence, total heat supplied is converted to work done by the gas (mechanical energy) which is an possible by second law of thermodynamics.
(c) When the gas expands adiabatically from 2 3. it is not possible to return to the same state with out being heat supplied, h ence the process 3 to 1 cannot be adiabatic