Question

A heat engine produces 100 J of heat, does 30 J of work, and emits 70 J into a cold reservoir. What is the efficiency of the heat engine?

• A. 100%
• B. 70%
• C. 42%
• D. 40%
• E. 30%

Answer 1

Answer: (E)

30%

The efficiency of heat engine is $\eta =\frac{W}{Q_{in}}$

Here work done , $W=30J$ and heat produced $Q_{in}=100J$

Thus, % of efficiency, $\eta =\frac{30}{100}\times 100=30$ %