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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.
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Solution
From the observations made (parts A and B) on the basis of Einstein’s photoelectric equation, we can draw the following conclusions:
- For surface A, the threshold frequency is more than 1015 HZ, hence no photoemission is possible.
- 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.
- For surface C, the threshold frequency is less than 1015 Hz. So photoemission occurs and photoelectrons have some kinetic energy.
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