$A$ photon of $300 \, nm$ is absorbed by a gas and then re-emits two photons. One re-emitted photon has a wavelength of $496 \, nm$. The wavelength of the second re-emitted photon is: (in $, nm$)

$A$ metal surface is exposed to solar radiation.

Choose the correct statements in reference to the photoelectric effect. $(i)$ There is no time lag between the striking of light and ejection of electrons from the metal surface. $(ii)$ The number of electrons ejected is independent of the intensity of light. $(iii)$ The elements $K$, $Rb$ and $Cs$ can show photoelectric effect when exposed to the beam of light.

Nitrogen laser produces a radiation at a wavelength of $337.1 \ nm$. If the number of photons emitted is $5.6 \times 10^{24}$,calculate the power of this laser.

Linear spectrum (line spectrum) is a characteristic of which of the following?

Calculate the wavelength,frequency and wave number of a light wave whose period is $2.0 \times 10^{-10} \,s$.