Question

Work function of Zn is $3.74$ eV. If the sphere of Zn is illuminated by the X-rays of wavelength $12\stackrel{o}{A}$, find the maximum potential production on the sphere, $h=6.625\times {10}^{-34}$Js.

Answer 1

Maximum kinetic energy of photo-electrons is

$K=\frac{hc}{\lambda }-\varphi$

$⟹K=\frac{6.625\times {10}^{-34}\times 3\times {10}^8}{12\times {10}^{-10}\times 1.6\times {10}^{-19}}-3.74eV$

$⟹K=1035eV-3.74eV\approx 1031eV$

When this much negative energy develops on the zinc sphere, even the fastest electron will have total energy zero and will not escape the sphere and no more charge is produced on the sphere as now no electron can leave the sphere surface.

This final potential of the sphere is the maximum potential .