Q: The work function of a photosensitive element is 2 eV. Calculate the velocity of a photoelectron when the element is exposed to a light of wavelength 4 × 10^{3} A° .

Sol: Einstein’s photoelectric equation is

$\large \frac{1}{2}m v^2 = \frac{h c}{\lambda} – W_0 $

$\large \frac{1}{2}m v^2 = \frac{6.62 \times 10^{-34}\times 3 \times 10^8}{4 \times 10^3} – 2 \times 1.6 \times 10^{-19} $

v = 6.228 x 10^{5} m/s.