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WORK SHEET - 6
Class 12 - Physics

1. A photo-cell connected in an electrical circuit is placed at a distance d from a source of light. As a result current I flows
in the circuit. What will be the current in the circuit when the distance is increased to 2d?

a) 4I b) I

c) I

4
d) 2I
2. As the intensity of incident light increases

a) the kinetic energy of emitted photoelectrons b) photoelectric current decreases

decreases

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c) photoelectric current increases d) the kinetic energy of emitted photoelectrons
increases
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3. The ratio of de-Broglie wavelength associated with two electrons accelerated through 25 V and 36 V is

a) 5

6
b) 36

25
14

c) d)
6 25

5 36

4. Two identical metal plates show photoelectric effect by a light of wavelength λ falls on plate A and λ on plate B
A B
28

( λA = 2λB ) . The maximum kinetic energy is:

KB
a) KA = 2KB b) KA =
2
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KB
c) K A
<
2
d) KA = KB

5. The correct graph representing the relation between energy (E) of photoelectrons and frequency ν of incident light is

a) b)

c) d)

6. Wavelength of light incident on a photo cell is 3000 A, if stopping potential is 2.5 volts, then work function of the
cathode of photocell is

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 a) 1.64 eV b) 2.41 eV

c) 4.56 eV d) 3.52 eV
7. Given: h = 6.6 ×10 −34
joule sec. The momentum of each photon in a given radiation is 3.3 ×10−29
kg metre/sec. The
frequency of radiation is

a) 1.5 ×10 13
Hz b) 1.8 ×10 13
Hz

c) 1.7 ×10 13
Hz d) 1.6 ×10 13
Hz
8. When ultraviolet rays incident on metal plate then photoelectric effect does not occur. It occurs by incidence of

a) X-rays b) Light waves

c) Radio waves d) Infrared rays

9. When the light of wavelength 300 nm (nanometer) falls on a photoelectric emitter, photoelectrons are liberated. For
another emitter, however, the light of 600 nm wavelength is sufficient for creating photoemission. What is the ratio of the
work functions of the two emitters?

a) 2 : 1 b) 1 : 4

c) 4 : 1 d) 1 : 2

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10. Photons of energy 3.2 eV are incident on a photosensitive surface. If the stopping potential for the emitted electrons is
1.5 V, the work function for the surface is:
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a) 3.2 eV b) 1.7 eV

c) 4.7 eV d) 1.5 eV
14

11. When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a
metal surface increases from 0.5 eV to 0.8 eV. The work function of the metal is
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a) 1.5 eV b) 1.0 eV

c) 1.3 eV d) 0.65 eV
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12. A photon of wavelength 663 nm is incident on a metal surface. The work function of the metal is 1.50 eV. The maximum
kinetic energy of the emitted photo electrons is

a) 3.0 × 10-20 J b) 4.5 × 10-20 J

c) 9.0 × 10-20 J d) 6.0 × 10-20 J

13. Photoelectrons are emitted by a metal surface only when

a) light is incident at an angle greater than the b) the wavelength of the incident light exceeds
critical angle a certain minimum value

c) frequency of the incident light exceeds a d) metal is initially charged

certain minimum value
14. Momentum of photon of wavelength λ is

a) hν

c
b) hλ

c) hλ

2
d) zero
c

15. A photocell connected in an electrical circuit is placed at a distance d from a source of light. As a result, current I flows
in the circuit. What will be the current in the circuit, when the distance is reduced to d/3?

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 a) 6I b) 1

3
I

c) I d) 9I
16. The momentum (in SI units) associated with a photon of energy 1.5 eV is:

a) 6 × 10 −29
b) 8 × 10
−28

c) 4 × 10 −27
d) 2 × 10
−30

17. Which one of the following metals does not exhibit emission of electrons from its surface when irradiated by visible
light?

a) Rubidium b) Caesium

c) Sodium d) Cadmium
18. Which of the following graphs correctly represents the variation of a particle momentum with its associated de-Broglie
wavelength?

a) b)

c)

18
d)
23
19. The cathode of a photoelectric cell is changed such that the work function changes from W1 to W2 (W2 > W1). If the
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currents before and after changes are I1 and I2, all other conditions remaining unchanged, then (assuming hν > W2),
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a) I1 = I2 b) I1 < I2

c) I1 < I2 < 2I1 d) I1 > I2

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20. In a photoelectric cell, the photoelectric current depends on the

a) wavelength of light b) potential difference applied

c) intensity of light d) frequency of light

21. An electron of mass m and charge e is accelerated from rest through a potential difference V in vacuum. Its final velocity
will be
−
−−
a) b)
eV
eV
√
2 m m

−−−
c) √ d)
eV
2eV
m
m

22. A photon of energy 7 eV is incident on a metal surface having the work function of 3.75 eV. The stopping potential is:

a) 1.75 eV b) 3.25 eV

c) 2.45 eV d) 3.75 eV
23. The wavelength associated with an electron accelerated through a potential difference of 100 V is of the order of

a) o b) o
1.2 A 10.5 A

c) d)

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 o o
1000 A 100 A
∘

24. The threshold wavelength for photoelectric emission from a material is 5200 A. Photoelectrons will be emitted when this
material is illuminated with monochromatic radiation from a:

a) 1 watt ultraviolet lamp b) 1 watt infrared lamp

c) 50 watt infrared lamp d) 1000 watt infrared lamp

25. The number of photo-electrons emitted for the light of a frequency ν (higher than the threshold frequency ν ) is 0

proportional to

a) ν − ν 0 b) Threshold frequency (ν ) 0

c) Intensity of light d) Frequency of light (ν )

26. Consider an electron in the nth orbit of a hydrogen atom in the Bohr model. The circumference of the orbit can be
expressed in terms of de Broglie wavelength λ of that electron as

a) nλ b) (0.529)nλ

−
c) √nλ d) (13.6)λ

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27. Specify the transition of electron in the wavelength of the line in the Bohr model of hydrogen atom which gives rise to
the spectral line of highest wavelength.
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a) n = 4 to n = 1 b) n = 3 to n = 2

c) n = 3 to n = 1 d) n = 4 to n = 2
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28. If the electron in the hydrogen atom jumps from the third orbit to the second orbit, the wavelength of the emitted
radiation in terms of the Rydberg constant is

a) 64
b) 6
28

7R 5R

c) d)
7 36

5R 5R

29. In Bohr’s model of hydrogen atom, the total energy of the electron in nth discrete orbit is proportional to
84

a) n2 b)
1

c) d) n
1

2
n

30. An electron orbiting in H atom has energy level -3.4 eV Its angular momentum will be:

a) 4 × 10-20 Js b) 2.1 × 1020 Js

c) 4 × 10-34 Js d) 2.1 × 10-34 Js

∘

31. A hydrogen atom in the ground state is excited by monochromatic radiation of λ = 975 A. Number of spectral lines in
the resulting spectrum emitted will be

a) 10 b) 6

c) 3 d) 2
32. When the hydrogen atom is in first excited level, its radius is

a) same b) four times

c) half d) twice

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33. The transition of electron that gives rise to the formation of the second spectral line of the Balmer series in the spectrum
of hydrogen atom corresponds to:

a) nf = 2 and ni = ∞ b) nf = 2 and ni = 3

c) nf = 3 and ni = 4 d) nf = 2 and ni = 4

34. The ratios between Bohr radii are

a) 1 : 4 : 9 b) 1 : 3 : 5

c) 2 : 4 : 6 d) 1 : 2 : 3
35. The ionisation energy of a hydrogen atom is 13.6 eV, the ionisation energy of a singly ionised helium atom would be

a) 13.6 eV b) 27.2 eV

c) 54.4 eV d) 6.8 eV
36. The wavelength of Lyman series for first member is
7

a) b)
3 7 4×1.097×10
× 1.097 × 10 m m
4 3

c) 4
7
m d) 4
7
m
3×10.97×10 3×1.097×10

18
37. A set of atoms in an excited state decays

a) into a lower state only when excited by an b) to emit photons only when they collide
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external electric field

c) in general to any of the states with lower d) all together simultaneously into a lower
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energy state
38. The potential energy of an electron in the second excited state in hydrogen atom is:
28

a) - 3.4 eV b) -6.8 eV

c) -3.02 eV d) -1.51 eV
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39. Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in
place of the gold foil. (Hydrogen is a solid at temperatures below 14 K.) What results do you expect?

a) There would be no large-angle scattering b) There would be scattering at 90∘

c) There would be scattering at all angles d) There would be no scattering

40. If an α-particle of mass m, charge q and velocity v is incident on a nucleus of charge Q and mass m, then the distance of
closest approach is
2
Qq
a) 2
b) Qqmv

mv 2

Qq Qq
c) 2 2
d) 2
4πε0 m v 4πε0 mv

41. The 20 cm radiowave emitted by hydrogen in interstellar space is due to the interaction, called the hyperfine interaction
in atomic hydrogen. The energy of the emitted wave is nearly

a) 7 × 10-15 J b) 7 × 10-8 J

c) 10-17 J d) 10-24 J

42. In the following transitions of the hydrogen atom, the one which gives an absorption line of highest frequency is

a) n = 1 to n = 2 b) n = 2 to n = 1

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 c) n = 3 to n = 8 d) n = 8 to n = 3
43. In terms of Rydberg constant R, the wavenumber of the first Balmer line is

a) b) 3R
5R

36

c) d) R
8R

44. Using the Bohr’s model, calculate the orbital period of the electron in a hydrogen atom in the n = 1 level.

a) 1.42 ×10 −16

s b) 3.62 ×10 −16
s

c) 1.52 ×10 −16

s d) 5.72 ×10 −16
s
45. The ionisation energy of H-atom is 13.6 eV. Following Bohr's theory, the energy corresponding to a transition between
the 3rd and the 4th orbit is

a) 0.85 eV b) 3.40 MeV

c) 0.66 eV d) 1.51 eV

46. The wavelengths of K X-rays for lead isotopes Pb208, Pb206, and Pb204 are λ
α 1, λ2 and λ respectively. Then
3

−−−−
a) λ 2 = λ1 λ3 b) λ2 = √λ1 λ3

18
λ1
c) λ 2
= d) λ2 = λ1 + λ3
λ3

47. In a hydrogen-like atom, electron makes the transition from an energy level with a quantum number n to another with a
quantum number (n - 1). If n >> X the frequency of radiation emitted is proportional to
23
a) 1
3
b) 1

n
n
14
c) 1
3
d) 1

n
2

2
n

48. The interplanar distance in a crystal is 2.8 × 10-8 sm. The value of maximum wavelength which can be diffracted is
28

a) 7.6 × 10-8 m b) 5.6 × 10-8 m

c) 1.4 × 10-8m d) 2.8 × 10-8 m

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49. If an electron in a hydrogen atom jumps from the 3rd orbit to the 2nd orbit, it emits a photon of wavelength λ . When it
jumps from the 4th orbit to the 3rd orbit, the corresponding wavelength of the photon will be

a) b)
16 20
λ λ
25 7

c) d)
20 9
λ λ
13 16

50. The energy of a hydrogen atom in its ground state is -13.6 eV. The energy of the level corresponding to the quantum
number n = 5 is

a) -0.85 eV b) -5.40 eV

c) -0.54 eV d) -2.75 eV
51. Assertion (A): When ultraviolet light is incident on a photocell, its stopping potential is V0 and the maximum kinetic
energy of the photoelectrons is Kmax. When the ultraviolet light is replaced by X-rays, both V0 and Kmax. increase.
Reason (R): Photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of
frequencies present in the incident light.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

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 c) A is true but R is false. d) A is false but R is true.
52. Assertion (A): In process of photoelectric emission, all emitted electrons do not have same kinetic energy.
Reason (R): If radiation falling on the photosensitive surface of metal consists of different wavelengths then energy
acquired by electrons absorbing photons of different wavelengths shall be different.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

53. Assertion (A): The de Broglie wavelength of a molecule varies inversely as the square root of temperature.
Reason (R): The root mean square velocity of the molecule depends on the temperature.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

54. Assertion (A): An electron and a photon possessing same wavelength, will have the same momentum.
Reason (R): Electron and photon possess same energy.

18
a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

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55. Assertion (A): The kinetic energy of photoelectrons emitted from metal surface does not depend on the intensity of
incident photon.
14

Reason (R): The ejection of electrons from metallic surface is not possible with the frequency of incident photons below
the threshold frequency.
28

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.
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c) A is true but R is false. d) A is false but R is true.

56. Assertion (A): On increasing the frequency of light, the photocurrent remains unchanged.
Reason (R): Photocurrent is independent of frequency but depends only on intensity of incident light.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

57. Assertion (A): The process of photoelectric emission is different to that of thermionic emission.
Reason (R): The process of thermionic emission is temperature-dependent but photoelectric emission is independent of
temperature.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

58. Assertion (A): If a proton and electron are moving with same velocity, then wavelength of de-Broglie wave associated
with electron is longer than that associated with proton.
Reason (R): The wavelength of de-Broglie wave associated with a moving particle is inversely proportional to its mass.

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 a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

59. Assertion (A): Photoelectric current increases with an increase in intensity of incident radiation, for a given frequency of
incident radiation and the accelerating potential.
Reason (R): Increase in the intensity of incident radiation results in an increase in the number of photoelectrons emitted
per second and hence an increase in the photocurrent.

a) Both Assertion (A) and Reason (R) are true b) Both Assertion (A) and Reason (R) are true,
and Reason (R) is the correct explanation of but Reason (R) is not the correct
the Assertion (A). explanation of the Assertion (A).

c) Assertion (A) is true, but Reason (R) is d) Assertion (A) is false and Reason (R) is also
false. false.
60. Assertion (A): Mass of moving photon varies inversely as the wavelength.
Reason (R): Energy of the particle = Mass × (speed of light)2

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the

18
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

23
61. Assertion (A): An electron microscope is based on de Broglie hypothesis.
Reason (R): A beam of electrons behaves as a wave that can be converted by electric and magnetic lenses.
14

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.
28

c) A is true but R is false. d) A is false but R is true.

62. Assertion (A): If the frequency of the incident light on a metal surface is doubled, the kinetic energy of emitted electrons
84

is more than doubled.

Reason (R): The metal will provide additional energy to the emitted photoelectron for light of higher frequency than that
for lower frequency.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

63. Assertion (A): The electrons and protons having same momentum has same de Broglie wavelength.
Reason (R): de Broglie wavelength λ .
h
=
p

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

64. Assertion (A): Photoelectric process is instantaneous process.
Reason (R): When photons of energy (hv) greater than work function of metal (ϕ ) are incident on a metal, the electrons
0

from metal are emitted with no time lag.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the

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 explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

65. Assertion (A): As work function of a material increases by some mechanism, it requires greater energy to excite the
electrons from its surface.
Reason (R): A plot of stopping potential (Vs) versus frequency (ν) for different materials, has greater slope for metals
with greater work functions.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

66. Assertion (A): Electrons in an atom are held by Colombian forces.
Reason (R): The atom is stable because the centripetal force due to Coulomb's law is balanced by the centrifugal force.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

18
67. Assertion (A): In the Bohr model of the hydrogen, atom, v and E represent the speed of the electron and the total energy
of the electron respectively. Then v/E is proportional to the quantum number n of the electron.
Reason (R): v ∝ n and E ∝ n-2.
23
a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.
14

c) A is true but R is false. d) A is false but R is true.

68. Assertion (A): According to Rutherford, atomic model, the path of an electron is parabolic.
28

Reason (R): Rutherford could not explain the stability of the atom.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
84

explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

69. Assertion (A): In alpha particle scattering experiment, thin gold foil was used.
Reason (R): Nucleus of gold is about 50 times heavier than an α-particle, it is reasonable to assume that it remains
stationary throughout the scattering process.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

70. Assertion (A): Hydrogen atom consists of only one electron but its emission spectrum has many lines.
Reason (R): Only Lyman series is found in the absorption spectrum of hydrogen atom whereas in the emission
spectrum, all the series are found.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

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71. Assertion (A): In the α-particle scattering experiment, most of the α-particles pass undeviated.
Reason (R): Most of the space in the atom is empty.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

72. Assertion: X-rays cannot be obtained from the hydrogen atom.
Reason: In a hydrogen atom difference between energy levels is of the order of 1 eV.

a) Assertion and reason both are correct b) Assertion and reason both are correct
statements and reason is correct explanation statements but reason is not correct
for assertion. explanation for assertion.

c) Assertion is correct statement but reason is d) Assertion is wrong statement but reason is
wrong statement. correct statement.
73. Assertion (A): Balmer series lies in the visible region of electromagnetic spectrum.
Reason (R): 1

λ
= R(
1
2
−
1

n
2
) , where n = 3, 4, 5.
2

18
a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

23
74. Assertion (A): In Lyman series, the ratio of minimum and maximum wavelength is .
3

Reason (R): Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of
14

hydrogen atom.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
28

explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

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75. Assertion (A): The force of repulsion between atomic nucleus and α-particle varies with distance according to inverse
square law.
Reason (R): Rutherford did α-particle scattering experiment.

a) Both A and R are true and R is the correct b) Both A and R are true but R is not the
explanation of A. correct explanation of A.

c) A is true but R is false. d) A is false but R is true.

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