Question

The work function for the following metals is given Na: 2.75 eV, K:2.30 eV , Mo: 4.17 eV , Ni: 515 eV.
Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 A from a `He-Cd` laser placed 1m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away?

Answer 1

Given `lambda = 3300 Å = 3300 xx10^(-10)` m
Energy of incident photon , `E = (hc)/lambda = (6.63 xx10^(-34) xx 3xx 10^(8))/(3300 xx10^(-10) xx1.6 xx10^(-19)):. E = 3.75 `ev
Here Na, K has work function than 3.75 eV. So they produce photoelectric effect . If the laser is brought nearer then only the intensity change or the number of photoelectrons change .