CBSE Class 12 Physics Dual Nature of Radiation and Matter MCQs Set C

Question. Characteristic X-rays are produced due to
(a) transfer of momentum in collision of electrons with target atoms
(b) transition of electrons from higher to lower electronic orbits of an atom
(c) heating of the target
(d) transfer of energy in collision of electrons with atoms in the target.

Answer : B

Question. A photon of energy 4 eV is incident on a metal surface whose work function is 2eV. The minimum reverse potential to be applied for stopping the emission of electrons is
(a) 2V
(b) 4V
(c) 6V
(d) 8V

Answer : A

Question. Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as
(a) f μ Z
(b) f μ Z2
(c) f μ Z
(d) f μ Z3/2

Answer : B

Question. Hard X-rays for the study of fractures in bones should have a minimum wavelength of 1011 m.
The accelerating voltage for electrons in X-ray machine should be
(a) < 124.2 kV
(b) > 124.2 kV
(c) Between 60 kV and 70 kV
(d) = 100 kV

Answer : A

Question. The number of photo electrons emitted for light of a frequency u (higher than the threshold frequency ν0) is proportional to
(a) threshold frequency (ν0)
(b) intensity of light
(c) frequency of light (ν)
(d) ν – ν0

Answer : B

Question. A 5 watt source emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of
(a) 8
(b) 16
(c) 2
(d) 4

Answer : D

Question. A photocell employs photoelectric effect to convert
(a) change in the frequency of light into a change in the electric current
(b) change in the frequency of light into a change in electric voltage
(c) change in the intensity of illumination into a change in photoelectric current
(d) change in the intensity of illumination into a change in the work function of the photocathode.

Answer : C

Question. A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then
(a) each emitted electron carries one quarter of theinitial energy
(b) number of electrons emitted is half the initial number
(c) each emitted electron carries half the initial energy
(d) number of electrons emitted is a quarter of the initial number.

Answer : D

Question. In which of the following, emission of electrons does not take place
(a) thermionic emission
(b) X-rays emission
(c) photoelectric emission
(d) secondary emission

Answer : B

Question. Thermions are
(a) protons
(b) electrons
(c) photons
(d) positrons.

Answer : B

Question. In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is
(a) 1.8 V
(b) 1.3 V
(c) 0.5 V
(d) 2.3 V

Answer : C

Question. A 5 watt source emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of
(a) 8
(b) 16
(c) 2
(d) 4

Answer : D

Question. Two radiations of photons energies 1 eV and 2.5 eV, successively illuminate a photosensitive metallic surface of work function 0.5 eV. The ratio of the maximum speeds of the emitted electrons is
(a) 1 : 4
(b) 1 : 2
(c) 1 : 1
(d) 1 : 5

Answer : B

Question. When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectrons and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively
(a) N and 2T
(b) 2N and T
(c) 2N and 2T
(d) N and T

Answer : B

Question. The threshold frequency for a photosensitive metal is 3.3 × 1014 Hz. If light of frequency 8.2 × 1014 Hz is incident on this metal, the cut-off voltage for the photoelectron emission is nearly
(a) 1 V
(b) 2 V
(c) 3 V
(d) 5 V

Answer : B

Question. The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function 5.01 eV, when ultraviolet light of 200 nm falls on it, must be
(a) 2.4 V
(b) –1.2 V
(c) –2.4 V
(d) 1.2 V

Answer : B

Question. Particle nature and wave nature of electromagnetic waves and electrons can be represented by :
(a) photoelectricity and electron microscopy
(b) light is refracted and diffracted
(c) X-rays is diffracted, reflected by thick metal sheet
(d) electrons have small mass, deflected by the metal sheet.

Answer : A

Question. The surface of zone material is radiated in turn by waves of l = 350 nm and 540 nm respectively.
The ratio of the stopping potential in the two cases is 2 : 1. The work function of the material is
(a) 4.20 eV
(b) 0.15 eV
(c) 2.10 eV
(d) 1.05 eV

Answer : D

Question. Light of wavelength 4000 Åis incident on a metal plate whose work function is 2eV. What is maximum kinetic energy of emitted photoelectron?
(a) 0.5 eV
(b) 1.1 eV
(c) 2.0 eV
(d) 1.5 eV

Answer : B

Question. A laser beam is used for carrying out surgery because it
(a) is highly monochromatic
(b) is highly coherent
(c) is highly directional
(d) can be sharply focussed

Answer : D

Question. Photoelectric emission occurs only when the incident light has more than a certain minimum
(a) power
(b) wavelength
(c) intensity
(d) frequency

Answer : D

Question. In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is
(a) 1.8 V
(b) 1.3 V
(c) 0.5 V
(d) 2.3 V

Answer : C

Question. When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectrons and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively
(a) N and 2T
(b) 2N and T
(c) 2N and 2T
(d) N and T

Answer : B

Question. When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occurs by incidence of
(a) infrared rays
(b) X-rays
(c) radio wave
(d) micro wave.

Answer : B

Question. A photocell employs photoelectric effect to convert
(a) change in the frequency of light into a change in the electric current
(b) change in the frequency of light into a change in electric voltage
(c) change in the intensity of illumination into a change in photoelectric current
(d) change in the intensity of illumination into a change in the work function of the photocathode.

Answer : C

Question. The photoelectric threshold wavelength of silver is 3250 × 10^–10 m. The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength 2536 × 10^–10 m is [Given h = 4.14 × 10^–15 eV s and c = 3 × 10⁸ m s^–1]
(a) ≈ 0.6 × 10⁶ m s^–1
(b) ≈ 61 × 10³ m s^–1
(c) ≈ 0.3 × 10⁶ m s^–1
(d) ≈ 6 × 10⁵ m s^–1

Answer : A, D

Question. A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then
(a) each emitted electron carries one quarter of the initial energy
(b) number of electrons emitted is half the initial number
(c) each emitted electron carries half the initial energy
(d) number of electrons emitted is a quarter of the initial number.

Answer : D

Question. When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occurs by incidence of
(a) infrared rays
(b) X-rays
(c) radio wave
(d) micro wave.

Answer : B

Question. A proton is about 1840 times heavier than an electron. When it is accelerated by a potential difference of 1 kV, its kinetic energy will be
(a) 1840 keV
(b) 1/1840 keV
(c) 1keV
(d) 920 V

Answer : C

Question. If an electron and a photon propagate in the form of waves having the same wavelength, it implies that they have the same
(a) energy
(b) momentum
(c) velocity
(d) angular momentum

Answer : B

Question. In photoelectric effect, the electrons are ejected from metals if the incident light has a certain minimum
(a) Wavelength
(b) Frequency .
(c) Amplitude
(d) Angle of incidence

Answer : B

Question. The stopping potential doubles when the frequency of the incident light changes from n to 3v/2. Then the work function of the metal must be
(a) hν/2
(b) hν
(c) 2hν
(d) none of the above

Answer : A

Question. Thermions are
(a) protons
(b) electrons
(c) photons
(d) positrons

Answer : B

Question. A source of light is placed at a distance of 50 cm from a photo cell and the stopping potential is found to be V0. If the distance between the light source and photo cell is made 25 cm, the new stopping potential will be :
(a) V₀/2
(b) V₀
(c) 4V₀
(d) 2V₀

Answer : B

Question. A photo-cell is illuminated by a source of light,which is placed at a distance d from the cell. If the distance become d/2, then number of electrons emitted per second will be
(a) remain same
(b) four times
(c) two times
(d) one-fourth.

Answer : B

Question. As the intensity of incident light increases
(a) kinetic energy of emitted photoelectrons increases
(b) photoelectric current decreases
(c) photoelectric current increases
(d) kinetic energy of emitted photoelectrons decreases.

Answer : C

Question. Number of ejected photoelectrons increases with increase
(a) in intensity of light
(b) in wavelength of light
(c) in frequency of light
(d) never.

Answer : A

Question. A photoelectric surface is illuminated successively by monochromatic light of wavelength l and l/2. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is (h = Planck’s constant, c = speed of light)
(a) 2hc/λ
(b) hc/3λ
(c) hc/2λ
(d) hc /λ

Answer : C

Question. The value of Planck’s constant is
(a) 6.63 × 10^–34 J/sec
(b) 6.63 × 10^–34 kg m2/sec
(c) 6.63 × 10^–34 kg m2
(d) 6.63 × 10^–34 J sec

Answer : D