In a photo-electic cell, a retarding potential of 0.5V is required to block the movement of electrons from the cathode when monochromatic light of wavelength 400 nm is incident on its surface. Find the work function of the material of the cathode.

Name a phenomenon or an experiment which proves.

(i)    Particle nature of electro-magnetic radiations.

(ii)    Wave nature of particles.

Monochromatic light of wavelength 198 nm is incident on the surface of a metal, whose work function is 2-5 eV. Calculate the stopping potential.

Energy levels of H atom are given by:

E_n  =  where n is Principal Quantum number. Calculate the wavelength of electromagnetic radiation emitted by hydrogen atom resulting from the transition: n = 2 to n = 1.