Q. For a sample of perfect gas when its pressure is changed isothermally from $p_i$ to $p_f$, the entropy change is given by
A) $\Delta S = nR\ln\left(\frac{p_f}{p_i}\right)$
B) $\Delta S = nR\ln\left(\frac{p_i}{p_f}\right)$
C) $\Delta S = nRT\ln\left(\frac{p_f}{p_i}\right)$
D) $\Delta S = RT\ln\left(\frac{p_i}{p_f}\right)$
Explanation
[Solution] Isothermal: $\Delta S = nR\ln\frac{V_f}{V_i} = nR\ln\frac{p_i}{p_f}$. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.