Light of same wavelength is incident on three photo-sensitive surfaces A,
B and C. The following observations are recorded.
(i) From surface A, photo electrons are not emitted.
(ii) From surface B, photo electrons are just emitted.
(iii) From surface C, photo electrons with some kinetic energy are emitted.
Compare the threshold frequencies of the three surfaces and justify your
answer.
Answers
Answer:
Order of threshold frequencies
(I)(A)>(II)(B)>(III)(C)
Explanation:
The energy of photon incident on surface should compensate the work function ( threshold energy) and also kinetic energy (if there exists)
(I) From surface A photo electrons are not emitted which means the photon energy was not able overcome threshold energy i.e the threshold energy is more than photon energy.
(II)From surface B photo electrons are just emitted (without any kinetic energy) . Therefore the threshold energy is equal(roughly) to photon energy.
(III)From surface c photons are emitted with kinetic energy i.e photon energy was able to provide threshold energy along with some kinetic energy i.e the photon has more energy than threshold energy.
Energy is directly proportional to frequency (E=hf) also since light with same wavelength is used photons used in (I), (II), (III) all have same energies.
therefore the order of threshold frequencies is
(I)>(II)>(III).
MISSION ACCOMPLISHED