NCERT Physics Class 12 Exemplar Ch 11 Dual Nature of Radiation and Matter Part 1 (For CBSE, ICSE, IAS, NET, NRA 2023)

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14 A proton and anα-particle are accelerated, using the same potential difference. How are the deBroglie wavelengths and related to each other?


15 (i) In the explanation of photo electric effect, we assume one photon of frequency ν collides with an electron and transfers its energy. This leads to the equation for the maximum energy of the emitted electron as

Where is the work function of the metal. If an electron absorbs 2 photons (each of frequency ν) what will be the maximum energy for the emitted electron?

(ii) Why is this fact (two photon absorption) not taken into consideration in our discussion of the stopping potential?


(ii) The probability of absorbing 2 photons by the same electron is very low. Hence such emissions will be negligible.

16 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.


  • In the first case energy given out is less than the energy supplied.
  • In the second case, the material has to supply the energy as the emitted photon has more energy.
  • This cannot happen for stable substances.

17 Do all the electrons that absorb a photon come out as photoelectrons?


  • No, most electrons get scattered into the metal. Only a few come out of the surface of the metal.

18 There are two sources of light, each emitting with a power of W. One emits X-rays of wavelength 1nm and the other visible light at nm. Find the ratio of number of photons of X-rays to the photons of visible light of the given wavelength?


  • Total E is constant
  • Let and be the number of photons of X-rays and visible region