Question

A real (non-Carnot) heat engine, operating between heat reservoirs at temperatures of and performs 4.3 kJ of net work and rejects of heat in a single cycle. The thermal efficiency of this heat engine is closest to

Answer 1

Complete Question

A real (non-Carnot) heat engine, operating between heat reservoirs at temperatures of 650 K and 270 K and performs 4.3 kJ of net work and rejects 8.00 kJ of heat in a single cycle. The thermal efficiency of this heat engine is closest to A) 0.35 B) 0.31. C) 0.28. D) 0.38. E) 0.42.

Answer:

The correct option is A

Explanation:

From the question we are told that

     The first operating temperature is  $T_1 = 650 \ K$

     The second operating temperature is  $T_2 = 270 \ K$

     The net workdone is  $W = 4.3 \ kJ = 4.3 *10^{3} \ J$( output of the engine )

     The amount of heat energy rejected is  $H = 8.00 \ kJ = 8.00 *10^{3 } \ J$

Generally a heat engine convert heat from a high temperature  to mechanical energy and then reject the remaining heat so the absorbed by the engine  is  

                          $W + H$

Generally the thermal  efficiency is mathematically represented as

     $\eta = \frac{out}{In} * 100$

Here out is the output of the engine

and  in is the input of the engine

      $\eta = \frac{W}{W + H} * 100$

=>   $\eta = \frac{4.3}{4.3 + 8} * 100$

=>   $\eta = 0.35$