Ncert Exercises & Solutions

12.7 A steam engine delivers 5.4×10 $^{8} J$ of work per minute and services 3.6 × 10 $^{9}$ J of heat per minute from its boiler. What is the efficiency of the engine? How much heat is wasted per minute?

The efficiency of the engine is given by:

$η = \frac{Output energy}{lnput energy}$

$\Rightarrow η = \frac{W}{H} = \frac{5.4 \times 10^{8}}{3.6 \times 10^{9}} = 0.15$

Hence, the percentage efficiency of the engine is 15 %.

Amount of heat wasted = 3.6 × 10 $^{9}$ – 5.4 × 10 $^{8}$ = 30.6 × 10 $^{8}$ = 3.06 × 10 $^{9}$ J

Therefore, the amount of heat wasted per minute is 3.06 × 10 $^{9}$ J.

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