Discussion Forum

Silver has a work function of 4.7 eV. When ultraviolet light of wavelength 100 nm is incident on it a potential of 7.7  V is required to stop the photoelectrons from reaching the collector plate. How much potential will be required to stop photoelectrons, when the light of wavelength 200 nm is incident on it?

Answer:

Explanation:

From Einsyein's photoelectric  equation,

$ev_{0}+\phi=\frac{hc}{\lambda}$

and $ev_{0}+\phi_{0}=\frac{hc}{\lambda'}$

$\frac{ev_{0}'+\phi}{eV_{0}+\phi}=\frac{\lambda}{\lambda'}=\frac{100}{200}=\frac{1}{2}$

$2ev_{0}'+2\phi=ev_{0}+\phi$

$ev_{0}'=\frac{ev_{0}-\phi}{2}=\frac{7.7-4.7}{2}=1.5V$