Question

What is the nature of change in internal energy in the following three thermodynamics cycles shown in figure?

• A. $\Delta U$ is positive in all the three cases
• B. $\Delta U$ is negative in all the three cases
• C. $\Delta U$ is positive for (i), negative for (ii), zero for (iii)
• D. $\Delta U=0$, in all the cases

Answer 1

The correct option is D $\Delta U=0$, in all the cases

Indicator diagrams shown in case (i), (ii) and (iii) are all closed.
$\therefore$ Each one represents a cyclic process
We know, in a cyclic process, system comes back to its original state.
$\therefore$ Change in internal energy $\left(\Delta U\right)=0$ ($\because$ internal energy is state function)
Therefore, in all the cases, $\Delta U=0$