# Physics MCQs for Class 12 with Answers Chapter 11 Dual Nature of Radiation and Matter

Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 11 Dual Nature of Radiation and Matter. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. Students can solve NCERT Class 12 Physics Dual Nature of Radiation and Matter MCQs Pdf with Answers to know their preparation level.

## Dual Nature of Radiation and Matter Class 12 Physics MCQs Pdf

Dual Nature of Radiation and Matter MCQ Questions with Answers Pdf Question 1. Light of frequency 1.9 times the threshold frequency is incident on a photosensitive material. If the frequency is halved and intensity is doubled, the photocurrent becomes
(b) doubled
(c) halved
(d) zero

Explaination: (d) As vi = 0.95 v0. No photoelectric emission takes place.

Dual Nature of Matter And Radiation Class 12 MCQ Question 2. Threshold wavelength for a metal having work function W0 is X. What is the threshold wavelength for the metal having work function 2W0?
(a) 4λ
(b) 2λ
(c) λ/2
(d) λ/4

Explaination:

MCQ on Dual Nature of Matter And Radiation Question 3. Radiations of frequency v are incident on a photosensitive metal. The maximum K.E. of the photoelectrons is E. When the frequency of the incident radiation is doubled, what is the maximum kinetic energy of the photoelectrons?
(a) 2E
(b) 4E
(c) E + hv
(d) E – hv

Explaination: (c) Using Einstein’s photoelectric equation hv – w0 = E

4. Maximum kinetic energy (Ek) of a photoelectron varies with frequency (v) of the incident radiation as

Explaination: (d) Using Einstein’s photoelectric equation hv = hv0 + Ek

Physics MCQs for Class 11 With Answers Pdf Question 5. The stopping potential V0 for photoelectric emission from a metal surface is plotted along y-axis and frequency v of incident light along x-axis. A straight line is obtained as shown. Planck’s constant is given by

(a) slope of the line
(b) product of the slope of the line and charge on electron
(c) intercept along y-axis divided by charge on the electron
(d) product of the intercept along x-axis and mass of the electron

Explaination: (b) Using Einstein’s photoelectric equation

6. The energy of photon of wavelength 450 nm is
(a) 2.5 × 10-17 J
(b) 1.25 × 10-17 J
(c) 4.4 × 10-19 J
(d) 2.5 × 10-19 J

Explaination:

7. The kinetic energy of an electron is 5 eV. Calculate the de broglie wavelength associated with it. (h = 6.6 × 10-34 Js, me = 9.1 × 10-31 kg)
(a) 5.47 Å
(b) 10.9 Å
(c) 2.7 Å
(d) None of these

Explaination:

Photoelectric Effect Multiple Choice Questions and Answers Pdf8. The slope of the stopping potential versus ‘ frequency graph for photoelectric effect is equal to

(a) h
(b) he
(c) h/e
(d) e

Explaination:
(c) Using Einstein’s equation for photoelectric effect

Class 12 Physics MCQ Chapter Wise Question 9. A proton and an α-particle are accelerated by the same potential difference. The ratio of their de broglie wavelengths (λp, λα) is
(a) 1
(b) 2
(c) √8
(d) $$\frac{1}{\sqrt{8}}$$

Explaination:

Class 12 Physics MCQ Chapter Wise Question 10. Work function of three metals A, B and C are 4.5 eV, 4.3 eV and 3.5 eV respectively. If a light of wavelength 4000 Å is incident on the metals then
(a) photoelectrons are emitted from A.
(b) photoelectrons are emitted from B.
(c) photoelectrons are emitted from C.
(d) photoelectrons are emitted from all the metals.

Explaination:
(d) Since energy of incident photon

11. Which of the following figure represents the variation of particle momentum and associated de Broglie wavelength?

Explaination:

12. According to Einstein’s photoelectric equation the plot of the kinetic energy of the emitted photo-electrons from a metal vs the frequency of the incident radiation gives a straight line whose slope
(a) depends on the nature of the metal used.
(b) depends on the intensity of the radiation.
(c) depends both on the intensity of the radiation and the metal used.
(d) is the same for all metals and independent of the intensity of the radiation.

Explaination: (d) Since slope = $$\frac{h}{e}$$

13. If K.E. of free electron is doubled, its de Broglie wavelength will change by factor
(a) $$\frac{1}{\sqrt{8}}$$
(b) √2
(c) $$\frac{1}{2}$$
(d) 2

Explaination:

14. For a given kinetic energy which of the following has smallest de Broglie wavelength?
(a) Electron
(b) Proton
(c) Deutron
(d) a-particle

Explaination:
(d) Since de Broglie wavelength

particle, mass of ∝-particle is maximum.

15. A particle is dropped from a height H. The de Broglie wavelength of the particle as a function of height is proportional to [NCERT Exemplar]

Explaination:

16. A proton, a neutron, an electron and an a-particle have same energy. Then their de Broglie wavelengths compare as [NCERT Exemplar]
(a)λp = λn > λe > λα
(b) λα < λp = λn < λe
(‘C) λe < λp = λn > λα
(d) λe = λp = λn = λα

Explaination:

17. In photoelectric effect what determines the maximum velocity of electron reacting the collector?
(a) Frequency of incident radiation alone
(b) Work function of metal
(c) Potential difference between the emitter and the collector
(d) All of these

Explaination: (d) As per Einstein’s photoelectric equation

18. A Proton and an a-particle have the same de Broglie wavelength. What is same for both of them?
(a) Mass
(b) Energy
(c) Frequency
(d) Momentum

Explaination: (d) Since λ = $$\frac{h}{p}$$, for the same wavelength momentum is also same.

19. The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nucleus with 1 MeV energy is nearly [NCERT Exemplar]
(a) 1.2 nm
(b) 1.2 × 10-3 nm
(c) 1.2 × 10-6 nm
(d) 1.2 × 101 nm

Explaination:

20. An electron is moving with an initial velocity v = v0i and is in a magnetic field B = B0 j. Then, its de Broglie wavelength [NCERT Exemplar]
(a) remains constant.
(b) increases with time.
(c) decreases with time.
(d) increases and decreases periodically.

Explaination:
(a) F = q(v × B) = F = qvB sin θ. As this force is perpendicular to v and B, so the magnitude of v will not change, i.e. momentum (p = mv) will remain constant in magnitude
De Broglie wavelength λ = $$\frac{h}{m v}$$ remams constant
∴ Comparing wavelengths of proton and neutron, mp = mn, hence λp = λn.

21. Who established that electric charge is quantised?
(a) J.J. Thomson
(b) William Crookes
(c) R.A. Millikan
(d) Wilhelm Rontgen

22. Cathode rays were discovered by
(a) Maxwell Clerk James
(b) Heinrich Hertz
(c) William Crookes
(d) J.J. Thomson

23. The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by which of the following physical processes?
(a) Thermionic emission
(b) Field emission
(c) Photoelectric emission
(d) All of these

24. The phenomenon of photoelectric emission was discovered in 1887 by
(a) Albert Einstein
(b) Heinrich Hertz
(c) Wilhelm Hallwachs
(d) Philipp Lenard

25. A metal surface ejects electrons when hit by green light but nothing when hit by yellow light. The electrons will be ejected when the surface is hit by
(a) blue light
(b) heat rays
(c) infrared light
(d) red light

26. Which of the following statements is correct regarding the photoelectric experiment?
(a) The photocurrent increases with intensity of light.
(b) Stopping potential increases with increase in intensity of incident light.
(c) The photocurrent increases with increase in frequency.
(d) All of these

27. In photoelectric effect, the photocurrent
(a) depends both on intensity and frequency of the incident light.
(b) does not depend on the frequency of incident light but depends on the intensity of the inci-dent light.
(c) decreases with increase in frequency of inci-dent light.
(d) increases with increase in frequency of inci-dent light.

28. The maximum value of photoelectric current is called
(a) base current
(b) saturation current
(c) collector current
(d) emitter current

29. In photoelectric effect, the photoelectric current is independent of
(a) intensity of incident light
(b) potential difference applied between the two electrodes
(c) the nature of emitter material
(d) frequency of incident light

30. In photoelectric effect, stopping potential depends on
(a) frequency of incident light
(b) nature of the emitter material
(c) intensity of incident light
(d) both (a) and (b)

31. According to Einstein’s photoelectric equation, the graph of kinetic energy of the photoelectron emitted from the metal versus the frequency of the incident radiation gives a straight line graph, whose slope
(a) depends on the intensity of the incident radi-ation.
(b) depends on the nature of the metal and also on the intensity of incident radiation.
(c) is same for all metals and independent of the intensity of the incident radiation.
(d) depends on the nature of the metal.

32. The figure shows stopping V0A potential V0 and frequency o for two different metallic surfaces A and B. The work function of A, as compared to that of B is

(a) less
(b) more
(c) equal
(d) nothing can be said

33. Which phenomenon best supports the theory that matter has a wave nature?
(a) Electron momentum
(b) Electron diffraction
(c) Photon momentum
(d) Photon diffraction

34. The figure shows the variation of photocurrent with anode potential for a photosensitive surface for three different radiations. Let Ia, Ib and Ic be the intensities and va, vb. and vcbe the frequencies for the curves a, b and c respectively. Then the correct relation is

(a) va = vb and Ia ≠ Ib
(b) va = vc and Ia = Ic
(c) va = vb and Ia = Ib
(d) vb = vc and Ib = Ic

35. The photoelectric effect can be explained by
(a) Corpuscular theory of light
(b) Wave nature of light
(c) Bohr’s theory
(d) Quantum theory of light

36. Work function of metal is
(a) the minimum energy required to free an electron from surface against coulomb forces.
(b) the minimum energy required to free an », nucleon.
(c) the minimum energy to ionise an atom.
(d) the minimum energy required to eject an electron orbit.

37. The rest mass of a photon of wavelength X is

38. Photoelectric effect is based on the law of conservation of
(a) energy
(b) mass
(c) linear momentum
(d) angular momentum

39. Einstein’s photoelectric equation is:

40. In photoelectric effect, the number of photoelectrons emitted is proportional to
(a) intensity of incident beam. –
(b) frequency of incident beam.
(c) velocity of incident beam.
(d) work function of photo cathode.

41. Which of the following shows particle nature of light?
(a) Photoelectric effect
(b) Refraction
(c) Interference
(d) Polarisation

42. Relativistic corrections become necessary when the expression for the kinetic energy 1/2 mv², becomes comparable with mc², where m is the mass of the particle. At what de Broglie wavelength, will relativistic corrections become important for an electron?
(a) λ = 10 nm
(b) λ = 10-1 nm
(c) λ = 10-4nm
(d) λ = 10-3 nm

43. Two particles A1 and A2 of masses m1, m2(m1 > m2) have the same de Broglie wavelength. Then,
(a) their momenta are the same.
(b) their energies are the same.
(c) energy of A1 is greater than the energy of A2
(d) energy of A1 is equal to the energy of A2

44. Photons absorbed in a matter are converted to heat. A source emitting h photon/sec of frequency v is used to convert 1 kg or ice at 0°C to water at 0°C. Then, the time T taken for the conversion
(a) increases with increasing n, with v fixed
(b) decreases with n fixed, v increasing.
(c) does not remain constant with n and v changing such that nv = constant
(d) increases when the product nv increases.

45. A particle moves in a closed orbit around the origin, due to a force which is directed towards the origin. The de Broglie wavelength of the particle varies cyclically between two values λ1, λ2 with λ1 > λ2. Which following statements are true?
(a) The particle could not be moving in a circular orbit with origin as centre.
(b) The particle could not be moving in an elliptic orbit with origin as its focus.
(c) When the de Broglie wavelength is λ1 the particle is nearer the origin than when its value is λ2.
(d) When the de Broglie wavelength λ2, the particle is nearer the origin than when its value λ1.

46. Consider the following statements:
I. According to de Broglie hypothesis, particles have wave-like characteristics.
II. When an electron and a proton have the same de Broglie wavelength, they will have equal momentum.
Which of the above statements is/are correct?
(a) I only
(b) II only
(c) both I and II
(d) neither I nor II

47. Maximum photoelectric current at particular intensity of incident radiation, which becomes independent of anode potential is known as __________ .

Explaination: saturation current

48. Stopping potential is of intensity of incident radiation but proportional to __________ of the radiation.

Explaination: independent, frequency

49. Kinetic energy and stopping potential are zero, when frequency of incident radiation is equal to __________ .

Explaination: threshold frequency

50. According to Planck’s quantum theory of radiation, an electromagnetic wave travels in the form packets of energy called __________ .

Explaination: photon

51. __________ experiment has varified and confirmed the wave nature of electrons.

Explaination: Davisson and Germer

52. Photoelectric emission occurs only when the frequency of incident radiation is __________ than threshold frequency.

Explaination: greater

53. Photoelectric emission is an __________ process.

Explaination: instantaneous

54. De Broglie wavelength associated with an electron beam accelerated through a potential difference V is __________ proportional to √V.

Explaination: inversely

55. __________ is the minimum amount of energy required to cause photoelectric emission.

Explaination: Wok function

56. Wave associated with the material particle is known as __________ .

Explaination: matter wave

57. Name the phenomenon which shows the quantum nature of electromagnetic radiation. [AI2017]

Explaination: Photoelectric effect.

58. Define the term ‘threshold frequency’ in relation to photoelectric effect. [Delhi 2019, Foreign 2011]

Explaination:
Threshold frequency: For every metal surface, there is a minimum frequency of incident radiation, below which the photoelectric emission does not take place no matter what the intensity of incident radiation is and for how long the radiations are allowed to fall on the metal. This frequency is called threshold frequency.

59. Show the variation of photocurrent with collector plate potential for different frequencies but same intensity of incident radiation. [AI 2017, Foreign 2011]

Explaination:
For same intensity but different frequencies v1 > v2 > v3 of incident radiation.

60. In photoelectric effect, why should the photoelectric current increases as the intensity of monochromatic radiation incident on a photosensitive surface is increased? Explain. [Foreign 2014]

Explaination:
An increase in intensity means increase in number of photons and thus, increase in photoelectric current.

61. Show the variation of photocurrent with collector plate potential for different intensities but same frequency of incident radiation. [Delhi 2019, AI 2017, Foreign 2011]

Explaination:

62. What is the rest mass of a photon?

Explaination: The rest mass of a photon is zero.

63. The given graph shows the variation of photoelectric current (I) versus applied voltage (V) for two different photosensitive materials and for two different intensities of the incident radiation. Identify the pairs of curves that correspond to different materials but same intensity of incident radiation. [Delhi 2013]

Explaination: The materials with same intensity of incident light are 1 and 3; 2 and 4.

64. 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. [Chennai 2019, Dehradun 2019]

Explaination:
As threshold frequency of metal A is greater, its work function, Φ = hv0, will also be greater than that of B.

65. For a given photosensitive material and with a source of constant frequency of incident radiation, how does the photocurrent vary with the intensify of incident light? [Delhi 2014, AI 2011C]

Explaination:
The photoelectric current increases linearly with the intensity of light as shown in the figure.

66. Ultraviolet radiations of different frequencies v1 and v2 are incident on two photosensitive materials having work functions W1 and W2 (W1 > W2) respectively. The kinetic energy of the emitted electrons is same in both the cases. Which one of the two radiations will be of higher frequency?

Explaination:
v1 > v2. As W1 > W2 and K.E. is same. From the relation,
hv = hv0 + $$\frac{1}{2}$$ mv²
and hv0 = W= work function

67. Two beams, one of red light and the other of blue light, of the same intensity are incident on a metallic surface to emit photoelectrons. Which one of the two beams emits electrons of greater kinetic energy? [HOTS]

Explaination:
The blue light emits the electrons of greater K.E., as vb > vr.

68. Can non-metals show photoelectric effect? [HOTS]

Explaination: Yes, when they are exposed to electromagnetic radiations of higher frequency.

69. A photosensitive surface emits photoelectrons when red light falls on it. Will the surface emit photoelectrons when blue light is incident on it? Give reason. [Foreign 2017]

Explaination:
Since condition for photoemission is $$\frac{h c}{\lambda} \geq \phi_{0}$$ (work function) and λB < λR hence, surface will emit photoelectrons.

70. What happens to the wavelength of a photon after it collides with an electron?

Explaination: The wavelength of a photon increases.

71. State de Broglie hypothesis. [Delhi 2012]

Explaination:
“Particles of matter moving with a given velocity (momentum) can display wave-like properties”.
$$\lambda=\frac{h}{p}$$

72. 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. [AI2013]

Explaination:
De Broglie wavelength associated with a charged particle when accelerated by a potential V is given by
$$\lambda=\frac{h}{p}=\frac{h}{\sqrt{2 m q V}}$$
where m = mass of charge particle and q = charge on the particle

73. A proton and an electron have same kinetic energy. Which one has smaller de Broglie wavelength and why? [AI 2012]

Explaination:

74. Show on a graph the variation of the de Broglie wavelength (λ) associated with an electron with the square root of accelerating potential (V). [Delhi 2019, Similar Panchkula 2019, Foreign 2012]

Explaination:

75. Write the relationship of de Broglie wavelength λ associated with a particle of mass m in terms of its kinetic energy E. [Delhi 2011C]

Explaination:
The required relation is given by $$\lambda=\frac{h}{\sqrt{2 m E}}$$

76. Name an experiment which shows wave nature of electrons. Which phenomenon was observed in this experiment using an electron beam?

Explaination:
Experiment: Davisson and Germer
Phenomenon: Diffraction

77. Two lines, A and B, in the plot given below show the variation of de Broglie wavelength, λ versus 1/√V, where V is the accelerating potential difference, for two particles carrying the same charge. Which one of two represents a particle of smaller mass?

Explaination:

78. The de Broglie wavelength of a particle of kinetic energy K is λ. What would be the wavelength of the particle, if its kinetic energy were K/4 [HOTS]

Explaination:

79. An electron and alpha particle have the same kinetic energy. How are the de Broglie wavelength associated with them related? [Similar Delhi 2019]

Explaination:

80. Two metals A and B have work functions 2 eV and 5 eV respectively. Which metal has lower threshold wavelength?

Explaination:
Metal with work function 5 eV has lower threshold wavelength, i.e. metal B.

81. Show graphically how the maximum kinetic energy of electrons emitted from a photosensitive surface varies with the frequency of incident radiations.

Explaination:

82. What is the charge on metal in the photoelectric experiment?

Explaination: It will possess positive charge as it has lost electrons.

83. What is the momentum of a photon of
(i) frequency v, and (ii) wavelength λ?

∴ Momentum of a photon = mc = $$\frac{hv}{c}$$
(ii) The momentum of a photon of wavelength λ is p = $$\frac{h}{\lambda}$$.