A metal surface of work function $1.13 \mathrm{eV}$ is irradiated with light of wavelength $310…
A metal surface of work function $1.13 \mathrm{eV}$ is irradiated with light of wavelength $310 \mathrm{~nm}$. The retarding potential required to stop the escape of photoelectrons is [Take $\frac{\mathrm{hc}}{}=1240 \times 10^{-9} \mathrm{SI}$ units]
$1 \cdot 13 \mathrm{~V}$
$2.87 \mathrm{~V}$
$3.97 \mathrm{~V}$
$4.23 \mathrm{~V}$
Solution
Energy of incident light:
$\begin{aligned}
E & =\frac{h c}{\mathrm{e} \lambda} \\
& =\frac{1240 \times 10^{-9}}{310 \times 10^{-9}} \\
& =4 \mathrm{ev}
\end{aligned}$
Stopping potential $\mathrm{V}_0=\frac{\mathrm{hc}}{\mathrm{e} \lambda}-\frac{\phi_0}{\mathrm{e}}$
$\mathrm{V}_0=4-1.13=2.87 \mathrm{~V}$