Q: A metal of work function 4 eV is exposed to a radiation of wavelength 140 ×10^{-9 }m. Find the stopping potential developed by it.

Sol: $\large E = \frac{h c}{\lambda } $

$\large E = \frac{6.62\times 10^{-34}\times 3 \times 10^8}{140 \times 10^{-9}\times 1.6 \times 10^{-19} } eV$

E = 8.86 eV

Work function , W_{0} = 8.86 – 4 = 4.86 eV

Stopping potential, V_{0} = 4.86 V