If the energy of a photon is $25\, eV$ and the work function of the material is $7\, eV$,then the value of the stopping potential is :-................. $V$

Sodium and copper have work functions $2.3 \ eV$ and $4.5 \ eV$ respectively. Then the ratio of their threshold wavelengths is nearest to

Two identical photocathodes receive light of frequencies $f_{1}$ and $f_{2}$ respectively. If the velocities of the photo-electrons emitted are $v_{1}$ and $v_{2}$ respectively,then:

The graph of maximum kinetic energy $(K.E._{max})$ against the frequency $(
u)$ of incident light is as shown in the figure. The slope of the graph and the intercept on the $X$-axis respectively are:

$A$ beam of light of wavelength $\lambda$ falls on a metal having work function $\phi$ placed in a magnetic field $B$. The most energetic electrons,moving perpendicular to the field,are bent in circular arcs of radius $R$. If the experiment is performed for different values of $\lambda$,then the $B^2$ vs. $\frac{1}{\lambda}$ graph will look like (keeping all other quantities constant):