\(E = h\upsilon = {E_3} - {E_1} = \) \(\frac{{ - 13.6}}{{{3^2}}} - \left( {\frac{{ - 13.6}}{{{1^2}}}} \right)\)
\({=\frac{-13.6}{9}+13.6=12.1 \,\mathrm{eV}}\)
Therefore, stopping potential
\(e{V_0} = h\upsilon - {\phi _0}\)
\( = 12.1 - 5.1\) [ \(\because \) work function \({{\phi _0} = 5.1}\) ]
\({V_0} = 7\,{\text{V}}\)
[Rhc=13.6 eV, $\mathrm{hc}=1242 \mathrm{eV} \mathrm{nm}, \mathrm{h}=6.6 \times 10^{-34} \mathrm{J-s}$ અને હાઈડ્રોજન પરમાણુનું દળ $\sim 1.6 \times 10^{-27} \mathrm{~kg}$ લો.]