Photoelectrons are emitted when photons of energy 4.2 eV are incident on a photosensitive metallic sphere of radius 10 ~cm and work function 2.4 eV . The number of photoelectrons emitted before the emission is stopped is [ 1 4 ₀ =9 10^9 SI unit; e =1.6 10⁻¹⁹ C ]

Step-by-step solution

h v=4.2 eV , =2.4 eV ,( KE )_ =4.2-2.4=1.8 eV The electrons will not be able to escape from the surface when its potential becomes 1.8 ~V . aligned & V = 1 4 ₀ q r & 1.8=9 10^9 q 0.1 & q =2 10⁻¹¹ C aligned The number of photoelectrons emitted before the emission is stopped is, n = q e = 2 10⁻¹¹ 1.6 10⁻¹⁹ =1.25 10^8