Question

Radiation of frequency 10¹⁵ Hz is incident on three photosensitive surfaces A, B and C. Following observations are recorded:

Surface A: no photoemission occurs

Surface B: photoemission occurs but the photoelectrons have zero kinetic energy.

Surface C: photo emission occurs and photoelectrons have some kinetic energy.
Using Einstein’s photo-electric equation, explain the three observations.

Answer 1

From the observations made (parts A and B) on the basis of Einstein’s photoelectric equation, we can draw the following conclusions:

1. For surface A, the threshold frequency is more than 10¹⁵ HZ, hence no photoemission is possible.
2. For surface B the threshold frequency is equal to the frequency of given radiation. Thus, photo-emission takes place but the kinetic energy of photoelectrons is zero.
3. For surface C, the threshold frequency is less than 10¹⁵ Hz. So photoemission occurs and photoelectrons have some kinetic energy.