با استفاده از معادلهی فوتوالکتریک، داریم:
${{K}_{\max }}=hf-{{W}_{{}^\circ }}\xrightarrow{{{W}_{{}^\circ }}=h{{f}_{{}^\circ }}}{{K}_{\max }}=hf-h{{f}_{{}^\circ }}\Rightarrow$
$ \left\{ \begin{matrix} {{({{K}_{\max }})}_{1}}=2h{{f}_{{}^\circ }}-h{{f}_{{}^\circ }}=h{{f}_{{}^\circ }}=4eV \\ {{({{K}_{\max }})}_{2}}=2/44h{{f}_{{}^\circ }}-h{{f}_{{}^\circ }}=1/44h{{f}_{{}^\circ }}=(1/44\times 4)eV \\ \end{matrix} \right.$
$\Rightarrow \frac{{{({{K}_{\max }})}_{2}}}{{{({{K}_{\max }})}_{1}}}={{\left( \frac{{{v}_{2}}}{{{v}_{1}}} \right)}^{2}}\Rightarrow \frac{1/44\times 4}{4}={{\left( \frac{{{v}_{2}}}{{{v}_{1}}} \right)}^{2}}\Rightarrow \frac{{{v}_{2}}}{{{v}_{1}}}=1/2$