Light of wavelength $4000 Å$ is incident on a sodium surface for which the threshold wavelength of photoelectrons is $5420 Å$. The work function of sodium is (in $eV$)

$A$ photocell is illuminated by a small source of light placed at a distance of $1 \ m$. When the same source of light is placed at a distance of $1/2 \ m$,the number of electrons emitted by the photocathode will .......

$A$ photocell is illuminated by a small bright source placed $d \; m$ away. When the same source of light is placed $\frac{d}{2} \; m$ away,the number of electrons emitted by the photocathode would

When the intensity of incident light increases:

Define saturation current,stopping potential,and cut-off frequency in the context of the photoelectric effect.

The time taken by a photoelectron to come out after the photon strikes is approximately