The ratio of the distance of $n^{\text {th }}$ bright band and $\mathrm{m}^{\text {th }}$ dark band from the central bright band in an interference pattern is

An ideal gas expands adiabatically, $(\gamma=1.5)$. To reduce the r.m.s. velocity of the molecules 4 times, the gas has to be expanded

Out of the following statements which is NOT the characteristics of electric lines of force?

The temperature at which oxygen molecules will have same r.m.s. speed as helium molecules at $57^{\circ} \mathrm{C}$ is (molecular masses of oxygen and helium are 32 and 4 respectively.)