Important Questions for Class 12 Chapter 11 - Dual Nature of Radiation and Matter

Important questions based on NCERT syllabus for Chapter 11 - Dual Nature of Radiation and Matter:

Question-1: There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength.

Solution:
If the materials absorb photons of shorter wavelength, then the energy of the incident photon on the material is high and the energy of emitted photon is low when it has a longer wavelength.
But, the energy of the incident photon is low for the substances which have to absorb photons of larger wavelength. Similarly, the energy of emitted photon is high to emit light of shorter wavelength. So, according to this statement material has to supply the energy for the emission of photons.
For a stable substance, it can’t be possible.

Question-2:
Do all the electrons that absorb a photon come out as photoelectrons?

Solution:
In photoelectric effect, most of the electrons get scattered into the metal by absorbing a photon. Therefore, all the electrons that absorb a photon don’t come out as photoelectron.

Question-3: Consider a beam of electrons (each electron with energy E) incident on a metal surface kept in an evacuated chamber. Then,
(a) No electrons will be emitted as only photons can emit electrons
(b) Electrons can be emitted but all with an energy, E
(c) Electrons can be emitted with any energy, with a maximum of E − Φ (Φ is the work function)
(d) Electrons can be emitted with any energy, with a maximum of E

Solution:

When a beam of electrons of energy E is incident on a metal surface kept in an evacuated chamber due to elastic collision electrons can be emitted with maximum energy E. When part of incident energy of electron is used in liberating the electrons from the surface of metal, then electrons can be emitted with energy less than E.