Dual Nature Of Radiation

Photoelectrons are emitted when photons of energy \(4.2 ~\mathrm{eV}\) are incident on a photosensitive metallic sphere of radius \(10 \mathrm{~cm}\) and work function \(2.4 ~\mathrm{eV}\). The number of photoelectrons emitted before the emission is stopped is

\(\left[\frac{1}{4 \pi \epsilon_0}=9 \times 10^9\right.\) SI unit; \(\left.\mathrm{e}=1.6 \times 10^{-19} \mathrm{C}\right]\)