When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the sat

Question

When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the saturation current and cut-off voltage are 12.0 mA and 0.5 V . If the same source is placed 0.4 m away from the photoelectric cell, then the saturation current and the stopping potential respectively are\

Professor PC Thomas Classes · Answer

The stopping potential or the cut-off voltage gives maximum kinetic energy of the electron. It depends on the material as well as the frequency of incident high whereas the current depends on the number of photons incident. Hence it is 0.5 V . By inverse square law, saturation current is inversely proportional to square of distance.\ $	herefore 12=\frac{\mathrm{K}}{(0.2)^{2}}$, initially\ or $I=\frac{K}{(0.4)^{2}}$, finally\ $	herefore \frac{\mathrm{I}}{12}=\frac{(0.2)^{2}}{(0.4)^{2}}=\frac{1}{4}$ or $\mathrm{I}=3 \mathrm{~mA}$\ $	herefore \mathrm{I}=3 \mathrm{~mA}$, potential $=0.5 \mathrm{~V}$