Q20 of 27 Page 87

In a refrigerator one removes heat from a lower temperature and deposits to the surroundings at a higher temperature. In this process, mechanical work has to be done, which is provided by an electric motor. If the motor is of 1kW power, and heat is transferred from –3°C to 27°C, find the heat taken out of the refrigerator per second assuming its efficiency is 50% of a perfect engine.

One thing to be noted is that Carnot engine is the most efficient engine. Its efficiency is given by,



Here,





According to question, its efficiency is 50% of a perfect engine which is a Carnot engine.


Efficiency





We know that,





As power of the motor is 1kW i.e. 1kJ/sec


Heat taken out of the refrigerator per second=19kJ.


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