question_answer

Radiation of frequency \[\mathbf{1}{{\mathbf{0}}^{\mathbf{15}}}\] Hz is incident on three photo-sensitive surfaces A, B and C. Following observations are recorded: Surface A: No photo-emission occurs. Surface B: Photo-emission occurs but the photo- electrons have zero kinetic energy. Surface C: Photo-emission occurs and photo- electrons have some K.E. Based on Einstein's photo-electric equation, explain the three observations.

Answer:

                                 From the observations made (parts A and B) on the basis of Einstein's photoelectric equation, we draw  following conclusions : 1. For surface A, the threshold frequency is more than \[\text{1}{{0}^{\text{15}}}\] Hz, hence no photo-emission is possible.   2. For surface B, the threshold frequency is equal to the frequency of given radiation.  Thus, photo-emission takes place but kinetic energy of photo-electrons is zero. 3. For surface C, the threshold frequency is less than \[\text{1}{{0}^{\text{15}}}\]  Hz.  So photo-emission occurs and photo-electrons have some kinetic energy.