Extra Questions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter

Q. 1. Name the phenomenon which shows the quantum nature of electromagnetic radiation.

Q. 2. Define intensity of radiation on the basis of photon picture of light. Write its SI unit.

Q. 3. The figure shows the variation of stopping potential V₀ with the frequency n of the incident radiations for two photosensitive metals P and Q. Which metal has smaller threshold wavelength? Justify your answer.

Q. 4. Write the basic features of photon picture of electromagnetic radiation on which Einstein’s
photoelectric equation is based.

Q. 5. Define the term ‘stopping potential’ in relation to photoelectric effect.

Q. 6. Define the term ‘threshold frequency’ in relations to photoelectric effects.

Q. 7. In photoelectric effect, why should the photoelectric current increase as the intensity of monochromatic radiation incident on a photosensitive surface is increased? Explain.

Q. 8. Write the expression for the de Broglie wavelength associated with a charged particle having charge ‘q’ and mass ‘m’, when it is accelerated by a potential V.

Q. 9. State de-Broglie hypothesis.

Q. 10. The figure shows a plot of three curves a, b, c showing the variation of photocurrent vs. collector plate potential for three different intensities I₁, I₂, and I₃ having frequencies n₁, n₂ and
n₃ respectively incident on a photosensitive surface.
Point out the two curves for which the incident radiations have same frequency but different intensities.

Q. 11. The stopping potential in an experiment on photoelectric effect is 1.5 V. What is the maximum kinetic energy of the photoelectrons emitted?

Q. 12. The maximum kinetic energy of a photoelectron is 3 eV. What is its stopping potential?

Q. 13. The stopping potential in an experiment on photoelectric effect is 2 V. What is the maximum kinetic energy of the photoelectrons emitted?

Q. 14. What is the stopping potential of a photocell, in which electrons with a maximum kinetic energy of 6 eV are emitted ?

Q. 15. The graph shows the variation of stopping potential with frequency of incident radiation for two photosensitive metals A and B. Which one of the two has higher value of work-function? Justify your answer.

Q. 16. An electron and a proton have the same kinetic energy. Which one of the two has the larger de Broglie wavelength and why?

Q. 17. Plot a graph showing variation of de-Broglie wavelength λ versus V₁ , where V is accelerating potential for two particles A and B carrying same charge but of masses m₁, m₂ (m₁ > m₂). Which one of the two represents a particle of smaller mass and why?

Q. 18. Show the variation of photocurrent with collector plate potential for different frequencies but same intensity of incident radiation.

Q. 19. (a) Draw a graph showing variation of photo-electric current (I) with anode potential (V) for different intensities of incident radiation. Name the characteristic of the incident radiation that is kept constant in this experiment.
(b) If the potential difference used to accelerate electrons is doubled, by what factor does the de-Broglie wavelength associated with the electrons change?

Q. 20. (a) Define the term ‘intensity of radiation’ in photon picture.
(b) Plot a graph showing the variation of photo current vs collector potential for three different intensities I₁ > I₂ > I₃, two of which (I₁ and I₂) have the same frequency ν and the third has frequency ν₁ > ν.
(c) Explain the nature of the curves on the basis of Einstein’s equation.

Q. 21. Show on a graph the variation of the de Broglie wavelength (λ) associated with an electron, with the square root of accelerating potential (V).

Q. 22. Two metals A and B have work functions 4 eV and 10 eV respectively. Which metal has the
higher threshold wavelength?

Q. 23. de Broglie wavelength associated with an electron accelerated through a potential difference V is λ What will be the de Broglie wavelength when the accelerating potential is increased to 4V ?

Q. 24. (a) Draw a graph showing variation of photocurrent with anode potential for a particular intensity of incident radiation. Mark saturation current and stopping potential.
(b) How much would stopping potential for a given photosensitive surface go up if the frequency of the incident radiations were to be increased from 4 × 10¹⁵ Hz to 8 × 10¹⁵ Hz?

Q. 25. 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?

Q. 26. Do all the electrons that absorb a photon come out as photoelectrons?

Q. 27. Electrons are emitted from a photosensitive surface when it is illuminated by green light but electron emission does not take place by yellow light. Will the electrons be emitted when the
surface is illuminated by (i) red light, and (ii) blue light?

Q. 28. In a photoelectric effect, the yellow light is just able to emit electrons, will green light emit
photoelectrons? What about red light?

Q. 29. Work function of aluminium is 4.2 eV. If two photons, each of energy 2.5 eV, are incident on its surface, will the emission of electrons take place? Justify your answer.

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