$A$ photon of $5.5 \ eV$ energy falls on the surface of a metal,emitting photoelectrons with a maximum kinetic energy of $4.0 \ eV$. The stopping voltage required for these electrons is .......... $V$.

When radiation of the wavelength $\lambda$ is incident on a metallic surface,the stopping potential is $4.8 \ V$. If the same surface is illuminated with radiation of double the wavelength,then the stopping potential becomes $1.6 \ V$. Then,the threshold wavelength for the surface is :

Photoelectric emission is observed from a metallic surface for frequencies ${\nu _1}$ and ${\nu _2}$ of the incident light rays $({\nu _1} > {\nu _2})$. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $1:k$,then the threshold frequency of the metallic surface is

By the photoelectric effect,Einstein proved:

If the threshold wavelength for sodium is $6800 \mathring{A}$,then the work function will be ............. $eV$.

In the photoelectric effect,the kinetic energy $(K.E.)$ of electrons emitted from the metal surface depends upon: