Question

Which, if any, of the heat engines in FIGURE EX 21.22 violate (a) the first law of thermodynamics or (b) the second law of thermodynamics? Explain.

Short answer

(b) violates first law of thermodynamics .

(a) violates the second law of thermodynamics .

Step-by-step solution

- Introduction (part a)First law of thermodynamics states that energy given to the system must be equal to total energy given out . In other words , energy is always conserved . Second law states that Carnot engine has maximum efficiency . 

Step-2

In (b) total energy input is 500 J and total energy output is 200 J + 200J = 400 J . It violates first law .

Efficiency of Carnot engine = $\frac{600-300}{600}\times 100=50\%$

efficiency of (a) = $\frac{300}{500}\times 100=60\%$. It is more than 50% , so it violates 2 nd law.

efficiency of (b) = $\frac{200}{500}\times 100=40\%$, it is less than 50% , so it does not violate .

efficiency of (c) = $\frac{100}{300}\times 100=33.33\%$, it is less than 50% , so it does not violate second law.

step 2  Second law of thermodynamics (part b)

Option (a)

Because efficiency has beyond the limiting efficiency, it violates the second rule of thermodynamics.