heat engine

[logistic_guy]

A heat engine exhausts $\displaystyle 8500 \ \text{J}$ of heat while performing $\displaystyle 2700 \ \text{J}$ of useful work. What is the efficiency of this engine?

 

[khansaheb]

A heat engine exhausts $\displaystyle 8500 \ \text{J}$ of heat while performing $\displaystyle 2700 \ \text{J}$ of useful work. What is the efficiency of this engine?

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[logistic_guy]

In the study of Thermodynamics, we have a beautiful conservation of energy formula.

$\displaystyle Q_H = Q_L + W$

$\displaystyle Q_H \rightarrow$ the total external heat energy supplied to the system during a cycle
$\displaystyle Q_L \rightarrow$ the wasted energy
$\displaystyle W \rightarrow$ the useful energy

Then, the efficiency of the system is:

$\displaystyle e = \frac{W}{Q_H} = \frac{W}{Q_L + W} = \frac{2700}{8500 + 2700} = 0.24$ or $\displaystyle \textcolor{blue}{24\%}$