A gas is found to obey the law $P =kV^a$. The initial temperature and volume are $V_0$. If the gas expands to $b V_0$ the sign of the internal energy change depends on which of the following? (Note: $\gamma$ is the adiabatic index)

Question

(A) $a, \gamma$ (B) $b, \gamma$ (C) $a, b$ (D) $a, b, \gamma$