Light of wavelength $4000 \ \mathring A$ is incident on a sodium surface,where the threshold wavelength for photoemission is $5420 \ \mathring A$. The work function of sodium is ............ $eV$.

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

$A$ photoelectric cell is illuminated by a point source of light $1 \ m$ away. When the source is shifted to $2 \ m$,then:

"With increase in frequency of light incident, number of electrons emitted increase" - True or false?

The following graph represents the variation of photocurrent with anode potential for a metal surface. Here $I_{1}, I_{2}$ and $I_{3}$ represent intensities and $\gamma_{1}, \gamma_{2}, \gamma_{3}$ represent frequencies for curves $1, 2$ and $3$ respectively,then

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