If Planck's constant is $6.63 \times 10^{-34} \mathrm{Js}$, then the slope of a graph drawn between cut-off voltage and frequency of incident light in a photoelectric experiment is

The graph given in the figure shows the variation of photo current $(I)$ and the applied voltage ( $V$ ) for two different materials and for two different intensities of the incident radiations. Then the curves which represent the same material are

Radiations of wavelength 400 nm incidents on a photosensitive material of work function 2.2 eV . The stopping potential is nearly

Consider two black bodies $A$ and $B$ having equal surface area. On the surface of $A, n$ photons of frequency $f$ are incident perpendicularly in a time $t$. On the surface of $B$, $2 n$ photons of frequency $3 f$ are incident perpendicularly in a time $4 t$. The ratio of average intensity of radiation on surface $A$ to that on surface $B$ is