Gas expanding adiabatically to temperature $T_2$. If $L_1$ and $L_2$ are lengths of the gas column before and after expansion respectively, then $\frac {T_1}{T_2}$ is given by
(a) $(\frac {L_1}{L_2})^\frac 23$
(b) $(\frac {L_1}{L_2})$
(c) $(\frac {L_2}{L_1})$
(d) $(\frac {L_2}{L_1})^\frac 23$
