Question

Which, if any, of the refrigerators in FIGURE EX21.23 violate (a) the first law of thermodynamics or (b) the second law of thermodynamics? Explain.

Short answer

Pump (c) will violate first law of thermodynamics .

Pump (b) will violate second law of thermodynamics.

Step-by-step solution

Step :1 Introduction (part a)

In pump ( c) , Total energy that is invoked is 50 J but energy output is only 40 J . So there is violation of conservation of energy . Hence first law is violated . In other pumps , no violation of first law is observed.

Step :2 Explanation (part b)

(b)The coefficient of performance is expressed as follows

$COP=\frac{300}{400-300}=3$

Hence there will not be more than 3 times withdrawal of heat from cold reservoir .

In pump (b) , energy input is 10 J and heat withdrawal is 40 J . So , there is 4 times heat withdrawal . It is more than 3 , the maximum COP , hence it violates the 2 nd law. The COP of other pumps is less than 3.

Step :3 Cold reservoir 

Calculating this coefficient for the three refrigerators we find values of $2,4,1.5$. Therefore it is clear that the second value is not violated in case of (a) and (c)