The light rays having photons of energy $4.2 \mathrm{eV}$ are falling on a metal surface having a work…
The light rays having photons of energy $4.2 \mathrm{eV}$ are falling on a metal surface having a work function of $2.2 \mathrm{eV}$. The stopping potential of the surface is:
$2 \mathrm{eV}$
$2 \mathrm{~V}$
$1.1 \mathrm{~V}$
$6.4 \mathrm{~V}$
Solution
By Einstein photoelectric equation, we have;
$\begin{aligned}
\text { K.E. } & =h v-\phi \\
e \mathrm{~V}_0 & =4.2 \mathrm{eV}-2.2 \mathrm{eV} \\
e \mathrm{~V}_0 & =2 \mathrm{eV}=2 \text { volt }
\end{aligned}$