Light source having wavelength 331 nm is used to generate photo-electrons whose stopping potential is 0.2 V. The work function of the used metal in…

Light source having wavelength $\displaystyle 331$ nm is used to generate photo-electrons whose stopping potential is $\displaystyle 0.2$ V . The work function of the used metal in the experiment is $\displaystyle \alpha \times 10^{-19} \mathrm{~J}$. The value of $\displaystyle \alpha$ is $\displaystyle \_\_\_\_$. ( $\displaystyle \mathrm{h}=6.62 \times 10^{-34} \mathrm{~J} \mathrm{~s}, \mathrm{e}=1.6 \times 10^{-19} \mathrm{C}$ and $\displaystyle \mathrm{c}=3 \times 10^8 \mathrm{~m} / \mathrm{s}$ )