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Question
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 ______.
- heat is completely converted to mechanical energy in such a process, which is not possible.
- mechanical energy is completely converted to heat in this process, which is not possible.
- curves representing two adiabatic processes don’t intersect.
- curves representing an adiabatic process and an isothermal process don’t intersect.
Solution
a and c
Explanation:
a. The given process is a cyclic process, i.e. it returns to the original state 1. And the change in internal energy in a cyclic process is always zero as for the cyclic process Uf = Ui. So, ∆U = Uf – Ui = 0
Hence, total heat is completely converted to mechanical energy. Such a process is not possible by the second law of thermodynamics.
c. Here, two curves are intersecting, when the gas expands adiabatically from 2 to 3. It is not possible to return to the same state without being heat supplied, hence the process 3 to 1 cannot be adiabatic. So, we conclude that such a process does not exist because curves representing two adiabatic processes do not intersect.
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