Question

When a metallic surface is illuminated with monochromatic light of wavelength $\lambda$, the stopping potential is $5 V_{0}$. When the same surface is illuminated with light of wavelength $3 \lambda$, the stopping potential is $V_{0}$. The work function of the metallic surface is $\frac{h c}{k \lambda}$. Find $k$.

Answer 1

$\frac{h c}{\lambda}=5 e V_{0}+\phi$
$\frac{h c}{3 \lambda}=e V_{0}+\phi$
$ \Rightarrow \frac{2 h c}{3 \lambda}=4 e V_{0} $
$\Rightarrow \phi=\frac{h c}{6 \lambda}$