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