\(eV{s_1} = \frac{{hc}}{{{\lambda _1}}} - h{v_0}\,\,\,\,\,\,\,\,\,......(1)\)
\( \Rightarrow \,\,e\left( {{V_{{S_1}}} + {V_{{S_1}}}} \right) = \frac{{hc}}{{{\lambda _1}}} - \frac{{hc}}{{{\lambda _2}}}\)
\(e{V_{{S_2}}} = \frac{{hc}}{{{\lambda _2}}} - h{v_0}\,\,\,\,\,\,\,\,\,\,......(2)\)
\( = 12400\,\,\left( {\frac{1}{{4000}} - \frac{1}{{3600}}} \right)\)
\( = 12400\,\,\left( {\frac{{ - 400}}{{4000 \times 3600}}} \right)\)
\( - \Delta {V_S} = \frac{{ - 12400}}{{3600}}volts\,\)
\( \Rightarrow \,\,\,\Delta {C_S} = \frac{{12400}}{{3600}} = 0.34\,volts\)