   Chapter 12, Problem 8CQ

Chapter
Section
Textbook Problem

A heat engine does work Weng while absorbing energy Qh from the hot reservoir and expelling energy Qc to the cold reservoir. Which one of the following is impossible? (a) |Qh| > |Qc| (b) |Qh| > Weng > |Qc| (c) |Qh| Weng = |Qc| (d) Weng > |Qh| (e) Weng > |Qh|

To determine
The impossible of one of the following (a) |Qh|>|Qc|>Weng , (b) |Qh|>Weng>|Qc| , (c) |Qh|>Weng=|Qc| , (d) Weng>|Qh| , and (e) Weng>|Qc| .

Explanation

For option (a):

Heat engine is an engine that takes in energy as heat and partially converts it into other forms like electrical and mechanical energies.

For a heat engine,

Weng=QhQc (1)

• Qc is the heat given to the cold reservoir
• Qh is the heat taken from the hot reservoir
• Weng is the work done by engine

The thermal efficiency of a heat engine is given by,

e=1|Qc||Qh| (2)

From the above equation, it is possible to have an engine with Qh>Qc>Weng . Because, here the efficiency is less than 1. so it is in accordance with The Second law of thermodynamics. Therefore, the given statement is possible.

For option (b):

From the above equation, it is possible to have an engine with Qh>Weng>Qc

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