The variation of stopping potential (V_o) as a function of the frequency (v) of the incident light for a metal is shown in figure, The work function of the surface is 

 

According to Einestein’s photo electric equation 
$$\begin{gathered} \mathrm{E}=\mathrm{\varphi }+{\mathrm{K}}_{max} \\ \text{ Where }\mathrm{\varphi }=\text{ work function }={\mathrm{h\nu }}_0 \\ {\mathrm{K}}_{max}=\mathrm{maximum}\mathrm{K}.\mathrm{E}\text{ of ejected photo electrons }={\mathrm{eV}}_0 \\ \mathrm{E}=\text{ energy of incident photon }=\mathrm{h\nu } \\ \begin{array}{l}\therefore \mathrm{h\nu }=\mathrm{\varphi }+{\mathrm{eV}}_0\\ {\mathrm{V}}_0=\frac{\mathrm{h}}{\mathrm{e}}\mathrm{v}-\frac{\mathrm{\varphi }}{\mathrm{e}}\\ \text{ From graph at }\mathrm{v}={\mathrm{v}}_0=5\times {10}^{14}\mathrm{Hz}, \mathrm{when} {\mathrm{V}}_0=0\mathrm{V}\\ \begin{array}{l}\mathrm{\varphi }=6.63\times {10}^{-34}\times 5\times {10}^{14}\mathrm{J}\\ \mathrm{\varphi }=\frac{6.63\times {10}^{-34}\times 5\times {10}^{14}}{1.6\times {10}^{-19}}\mathrm{eV}\\ \mathrm{\varphi }=2.07\mathrm{eV}\end{array}\end{array} \end{gathered}$$