A spring executes S.H.M. with mass 1 kg attached to it. The force constant of the spring is $4 \mathrm{~N} / \mathrm{m}$. If at any instant its velocity is $20 \mathrm{~cm} / \mathrm{s}$, the displacement at that instant is (Amplitude of S.H.M. is 0.4 m )

The material used for solar cell should have band gap

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