Question

The work function for the following metals is given: Na: 2.75 eV; K: 2.30 eV; Mo: 4.17 eV; Ni: 5.15 eV. Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away?

Answer 1

λ = 3300 = 3300 × 10-10m
Energy of a photon of incident light,

Since the work functions of MO and Ni are greater than the energy of the photon of incident light, photoelectric emission will not occur for these metals.

If the laser is brought nearer, the intensity of incident radiation on the metal will increase. It will increase the photo-emission in case of Na and K. However, no photo electric emission will take place in case of MO and N.