An observer moves towards a stationary source of sound with a velocity of one-fifth of the velocity of sound. The percentage increase in the apparent frequency is

A diatomic molecule has moment of inertia ' I ', By applying Bohr's quantization condition, its rotational energy in the $\mathrm{n}^{\text {th }}$ level is $[\mathrm{n} \geq 1]$ [h= Planck's constant]

The frequency of incident light falling on a photosensitive material is doubled, the K.E. of the emitted photoelectrons will be

A screen is placed at 50 cm from a single slit, which is illuminated with light of wavelength 600 nm . If separation between the $1^{\text {st }}$ and $3^{\text {rd }}$ minima in the diffraction pattern is 3 mm then slit width is