Question

A thermodynamic system undergoes a cyclic process as shown in the figure. In each of the loops 1 and 2, does the heat flow into or out of the system?

• A. into loop 1 and out of loop 2
• B. into loop 2 and out of loop 1
• C. into loop 1 and into loop 2
• D. out of loop 1 and loop 2 both

Answer 1

Answer: (A)

into loop 1 and out of loop 2

$\Delta U_{cycle}=0$

Thus from 1st law,

$Q_{cycle}=\Delta U_{cycle}+W_{cycle}$ where $\Delta U_1=0$

$⟹$ $Q_{cycle}=W_{cycle}$

Now in loop (1),

$W_{expansion}>W_{compression}$

$⟹W_{cycle}>0$

Thus $Q_1>0$

Hence heat flows into the system in loop 1.

Now in loop (2),

$W_{expansion}<W_{compression}$

$⟹W_{cycle}<0$

Thus , $Q_2<0$

Hence heat flows out of the system in loop 2.