Physics Class 12
Solutions to CBSE Sample Paper - Physics Class 12

Radiation of frequency 10 15 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.



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

  1. For surface A, the threshold frequency is more than 10 15 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 kinetic energy of photoelectrons is zero.
  3. For surface C, the threshold frequency is less than 10 15 Hz. So photoemission occurs and photoelectrons have some kinetic energy
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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.