Question

Based on the first law of thermodynamics, which one of the following is correct?

• A. For an isothermal process, $q=+w$
• B. For an isochoric process, $\Delta U=-q$
• C. For an adiabatic process, $\Delta U=-w$
• D. For a cyclic process, $q=-w$

Answer 1

The correct option is D For a cyclic process, $q=-w$

We know that $\Delta U=q+w$
For an isothermal process, $\Delta U=0$. Hence $q=-w$
For an isochoric process, $\Delta V=0$
$\therefore w=-p\Delta V=0$
Hence, $\Delta U=q$
For an adiabatic process, $q=0$
Hence, $\Delta U=w$
For a cyclic process, $\Delta U=0$.
Hence, $q=-w$