heat engine efficiency hard

Question

Heat engine absorbs Q_h and rejects Q_c per cycle. Efficiency is:

RankGuru · Accepted Answer

Efficiency ($\eta$) is defined as the useful work output per heat input:
$\eta = \frac{W}{Q_h}$
From conservation of energy in a cycle, the work done $W$ must be the net heat absorbed:
$W = Q_h - Q_{c}$ (where $Q_c$ is heat rejected).
$\eta = \frac{Q_h - Q_c}{Q_h} = 1 - \frac{Q_c}{Q_h}$.
Efficiency can only be $1$ ($100\%$) if $Q_c = 0$, which is forbidden by the Second Law.

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heat engine efficiency hard

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