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.)

A single slit diffraction pattern is formed with white light. For what wavelength of light the $4^{\text {th }}$ secondary maximum in diffraction pattern coincides with the $3^{\text {rd }}$ secondary maximum in the pattern of light of wavelength ' $\lambda$ '?