\(\left\{ {\frac{{ - e{V_0}}}{2} = hv - \phi } \right\} \times 2\) ..... \((1)\)
\( - e{V_0} = \frac{{hv}}{2} - \phi \) ..... \((2)\)
\(0 = 2hv - 2\phi - \frac{{hv}}{2} + \phi \)
\(\phi = \frac{{3hv}}{2}\) \( \Rightarrow {v_{th}} = \frac{{3v}}{2}\)
(પ્લાંક અચળાંક $\left. h =6.62 \times 10^{-34}\, J . s \right)$