Light of wavelength $\lambda$ strikes a photoelectric surface and electrons are ejected with energy E . If $E$ is to be increased to twice the original value, the wavelength changes to $\lambda_1$

For ideal non-rigid diatomic gas, the value of $\frac{\mathrm{R}}{\mathrm{C}_{\mathrm{V}}}$ is nearly $\left(\gamma=\frac{\mathrm{C}_{\mathrm{P}}}{\mathrm{C}_{\mathrm{V}}}=\frac{9}{7}\right)$

Two long straight wires A and B carrying equal current 'I' were kept parallel to each other at distance ' $d$ ' apart. Magnitude of magnetic force experienced by length $L$ of wire $A$ is ' $F$ '. If the distance between the wires is made half and currents are doubled, force $F_2$ on length $L$ of wire $A$ will be

There is head-on elastic collision between the two particles moving in the same direction with speeds $5 \mathrm{~m} / \mathrm{s}$ and $3 \mathrm{~m} / \mathrm{s}$ respectively. After collision, the velocity of the first particle becomes $4 \mathrm{~m} / \mathrm{s}$ in the same direction. The velocity of the second particle should be