Figure Fig. $19.16$ represents a graph of kinetic energy of most energetic photoelectrons ${\mathrm{K}}_{\max }$ (in $\mathrm{eV}$ ), and frequency (v) for a metal used as cathode in photoelectric experiment. The threshold frequency of light for the  photoelectric emission for the metal is 

The figure, Fig. $19.17$ shows variation of photocurrent with anode potential for a photo-sensitive surface for three different radiations. Let ${\mathrm{I}}_{{\mathrm{a}}^{\text{'}}}{\mathrm{I}}_{\mathrm{b}}$ and ${\mathrm{I}}_{\mathrm{c}}$ be the intensities and ${\mathrm{v}}_{{\mathrm{a}}^{\text{'}}}{\mathrm{v}}_{\mathrm{b}}$ and ${\mathrm{v}}_{\mathrm{c}}$ be the frequencies for the curves a, b and c respectively. Then 

In a photoelectric effect measurement, the stopping potential for a given metal is found to be ${\mathrm{V}}_0$ volt when radiation of wavelength ${\mathrm{\lambda }}_0$ is used. If radiation of wavelength $2{\mathrm{\lambda }}_0$ is used with the same metal then the stopping potential (in volts) will be

The threshold frequency for a metallic surface corresponds to an energy of $6.2\mathrm{eV}$ and the stopping potential for a radiation incident on this surface is $5 \mathrm{V}$. The incident radiation lies in

In a photoelectric effect experiment, the slope of the graph between the stopping potential and the incident frequency will be of the order of