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

Question. X-ray will not show the phenomenon of :
(a) interference
(b) deflection by electric field
(c) diffraction
(d) superposition

Answer : B

Question. Which one of the following is not dependent on the intensity of incident photon in a photoelectric experiment ?
(a) work function of the surface
(b) kinetic energy of photo-electron
(c) stopping potential
(d) amount of photo-electric current

Answer : B

Question. The kinetic energy of an electron, which is accelerated in the potential difference of 100 V, is :
(a) 1.6 × 10^–10 J
(b) 1.6 × 10⁸ J
(c) 1.6 × 10^–17 J
(d) 1.6 × 10^–18 J

Answer : C

Question. When cathode rays strike a metal target of high melting point with a very high velocity then which of the following are produced ?
(a) g-waves
(b) Ultrasonic
(c) X-rays
(d) a-rays

Answer : C

Question. Which of the following is not the property of cathode rays ?
(a) It produces heating effect.
(b) It does not deflect in electric field.
(c) It casts shadow.
(d) It produces fluorescence.

Answer : B

Question. Who evaluated the mass of electron indirectly with help of charge?
(a) Thomson
(b) Millikan
(c) Rutherford
(d) Newton

Answer : A

Question. In a discharge tube at 0.02 mm, there is formation of
(a) Crooke’s dark space
(b) Faraday’s dark space
(c) both space partly
(d) none of these.

Answer : A

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. The cathode of a photoelectric cell is changed such that the work function changes from W₁ to W₂ (W₂ > W₁). If the current before and after changes are I₁ and I₂, all other conditions remaining unchanged, then (assuming hu > W₂)
(a) I₁ = I₂
(b) I₁ < I₂
(c) I₁ > I₂
(d) I₁ < I₂ < 2I₁ 

Answer : A

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. In the phenomenon of electric discharge through gases at low pressure, the coloured glow in the tube appears as a result of
(a) collisions between the charged particles emitted from the cathode and the atoms of the gas
(b) collision between different electrons of the atoms of the gas
(c) excitation of electrons in the atoms
(d) collision between the atoms of the gas.

Answer : A

Question. In a discharge tube ionization of enclosed gas is produced due to collisions between
(a) neutral gas atoms/molecules
(b) positive ions and neutral atoms/molecules
(c) negative electrons and neutral atoms/molecules
(d) photons and neutral atoms/molecules.

Answer : C

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. 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. Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled?
(a) Doubled
(b) Four times
(c) One-fourth
(d) Zero

Answer : D

Question. The work function of a photosensitive material is 4.0 eV. The longest wavelength of light that can cause photon emission from the substance is (approximately)
(a) 3100 nm
(b) 966 nm
(c) 31 nm
(d) 310 nm

Answer : D

Question. When a metallic surface is illuminated with radiation of wavelength l, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2l, the stopping potential is V/4. The threshold wavelength for the metallic surface is
(a) 5/2 λ
(b) 3λ
(c) 4λ
(d) 5λ

Answer : B

Question. The work functions for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein’s equation the metals which will emit photoelectrons for a radiation of wavelength 4100 Å is/are
(a) A only
(b) A and B only
(c) all the three metals
(d) none.

Answer : B

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 photosensitive metallic surface has work function, hu₀. If photons of energy 2hu₀ fall on this surface, the electrons come out with a maximum velocity of 4 × 10⁶ m/s. When the photon energy is increased to 5hu₀, then maximum velocity of photoelectrons will be
(a) 2 × 10⁷ m/s
(b) 2 × 10⁶ m/s
(c) 8 × 10⁶ m/s
(d) 8 × 10⁵ m/s

Answer : C

Question. The force on a hemisphere of radius 1 cm if a parallel beam of monochromatic light of wavelength 500 nm. falls on it with an intensity of 0.5 W/cm², striking the curved surface in a direction which is perpendicular to the flat face of the hemisphere is (assume the collisions to be perfectly inelastic)
(a) 5.2 × 10^–13 N
(b) 5.2 × 10^–12 N
(c) 5.22 × 10^–9 N
(d) zeroAnswer

Answer : C

Question. A 15.0 eV photon collides with and ionizes a hydrogen atom. If the atom was originally in the ground state (ionization potential =13.6 eV), what is the kinetic energy of the ejected electron?
(a) 1.4 eV
(b) 13.6 eV
(c) 15.0 eV
(d) 28.6 eV

Answer : A

Question. A beam of cathode rays is subjected to crossed electric (E) and magnetic fields (B). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by
(a) B²/2VE²
(b) 2VB²/E²
(c) 2VE²/B²
(d) E²/2VB²

Answer : D

Question. In the phenomenon of electric discharge through gases at low pressure, the coloured glow in the tube appears as a result of
(a) collisions between the charged particles emitted from the cathode and the atoms of the ga
(b) collision between different electrons of the atoms of the gas
(c) excitation of electrons in the atoms
(d) collision between the atoms of the gas.

Answer : A

Question. Which of the following statement is correct?
(a) The photocurrent increases with intensity of light.
(b) The stopping potential increases with increase of incident light.
(c) The current in photocell increases with increasing frequency.
(d) The photocurrent is proportional to the applied voltage.

Answer : A

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. J.J. Thomson’s cathode-ray tube experiment demonstrated that
(a) cathode rays are streams of negatively charged ions
(b) all the mass of an atom is essentially in the nucleus
(c) the e/m of electrons is much greater than the e/m of protons
(d) the e/m ratio of the cathode-ray particles changes when a different gas is placed in the discharge tube

Answer : C

Question. Which of the following is not the property of cathode rays ?
(a) It produces heating effect.
(b) It does not deflect in electric field.
(c) It casts shadow.
(d) It produces fluorescence.

Answer : B

Question. When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is
(a) 0.65 eV
(b) 1.0 eV
(c) 1.3 eV
(d) 1.5 eV

Answer : B

Question. The work function of a surface of a photosensitive material is 6.2 eV. The wavelength of the incident radiation for which the stopping potential is 5 V lies in the
(a) Infrared region
(b) X-ray region
(c) Ultraviolet region
(d) Visible region.

Answer : C

Question. When photons of energy hu fall on an aluminium plate (of work function E0), photoelectrons of maximum kinetic energy K are ejected. If the frequency of radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be
(a) K + hu
(b) K + E0
(c) 2K
(d) K

Answer : A

Question. Photons with energy 5 eV are incident on a cathode C in a photoelectric cell. The maximum energy of emitted photoelectrons is 2 eV. When photons of energy 6 eV are incident on C, no photoelectrons will reach the anode A, if the stopping potential of A relative to C is
(a) +3 V
(b) +4 V
(c) –1 V
(d) –3 V

Answer : D

Question. Who evaluated the mass of electron indirectly with help of charge?
(a) Thomson
(b) Millikan
(c) Rutherford
(d) Newton

Answer : A

Question. In a discharge tube at 0.02 mm, there is formation of
(a) Crooke’s dark space
(b) Faraday’s dark space
(c) both space partly
(d) none of these.

Answer : A

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. When the light of frequency 2u0 (where u0 is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is v1. When the frequency of the incident radiation is increased to 5u0, the maximum velocity of electrons emitted from the same plate is v2. The ratio of v1 to v2 is
(a) 1 : 2
(b) 1 : 4
(c) 4 : 1
(d) 2 : 1

Answer : A

Question. In a discharge tube ionization of enclosed gas is produced due to collisions between
(a) neutral gas atoms/molecules
(b) positive ions and neutral atoms/molecules
(c) negative electrons and neutral atoms/molecules
(d) photons and neutral atoms/molecules.

Answer : C

Question. J.J. Thomson’s cathode-ray tube experiment demonstrated that
(a) cathode rays are streams of negatively charged ions
(b) all the mass of an atom is essentially in the nucleus
(c) the e/m of electrons is much greater than the e/m of protons
(d) the e/m ratio of the cathode-ray particles changes when a different gas is placed in the discharge tube

Answer : C

Question. Which of the following statement is correct?
(a) The photocurrent increases with intensity of light.
(b) The stopping potential increases with increase of incident light.
(c) The current in photocell increases with increasing frequency.
(d) The photocurrent is proportional to the applied voltage.

Answer : A

Question. A certain metallic surface is illuminated with monochromatic light of wavelength, l. The stopping potential for photoelectric current for this light is 3V0. If the same surface is illuminated with light of wavelength 2l, the stopping potential is V0. The threshold wavelength for this surface for photoelectric effect is
(a) λ/4
(b) λ/6
(c) 6l
(d) 4l

Answer : D