NCERT Solutions for class 12 Physics | Chapter 11 - Dual Nature of Radiation and Matter

(1) In photo electric emission, for alkali metals the threshold frequency lies in the:
[A] visible region
[B] ultraviolet region
[C] infrared region
[D] far end of the infrared region
Answer: visible region
(2) The charge of a photo electron is :
[A] 9.1 × 10-31 C
[B] 9.1 × 10-27 C
[C] 9.1 × 10-24 C
[D] none of these
Answer: none of these

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(3) What is the de-Broglie wavelength of an electron accelerated from rest through a potential difference of V volts?
[A]
[B]
[C]
[D] None of these
Answer: A
(4) X-rays are:
[A] deflected by an electric field
[B] deflected by a magnetic field
[C] deflected by both electric and magnetic fields
[D] not deflected by electric and magnetic fields
Answer: not deflected by electric and magnetic fields
(5) The work function of photoelectric material is 3.3 eV. The threshold frequency will be equal to:
[A] 8 × 1014 Hz
[B] 8 × 1010 Hz
[C] 5 × 1010 Hz
[D] 4 × 1014 Hz
Answer: 8 × 1014 Hz
(6) The ratio of specific charge of an alpha particle to the proton is:
[A] 1 : 2
[B] 2 : 1
[C] 4 : 1
[D] 1 : 4
Answer: 1 : 2
(7) Protons and alpha particles have the same de-Broglie wavelength. What is same for both of them ?
[A] Energy
[B] Time period
[C] Frequency
[D] Momentum
Answer: Momentum
(8) Millikan’s oil drop experiment makes use of:
[A] Stokes’ law
[B] Boyle’s law
[C] Gas equation
[D] Bernoulli’s theorem
Answer: Stokes’ law
(9) The number of photons of frequency n present in energy E, in terms of Planck’s constant h:
[A] E/nh
[B] nhE
[C] nh/E
[D] nE/h
Answer: E/nh
(10) Name the scientists who first studied the passage of electricity through fluids to establish the electrical nature of matter:
[A] Millikan
[B] Planck
[C] Faraday
[D] Boyle
Answer: Faraday
(11) The different stages of discharge in a discharge tube can be explained on the basis of:
[A] the wave nature of light
[B] the dual nature of light
[C] wave nature of electrons
[D] the collision between the charged particles emitted from the cathode the atoms of the gas in the tube
Answer: the collision between the charged particles emitted from the cathode the atoms of the gas in the tube
(12) The momentum of an electron that emits a wavelength of 2 Å. will be:
[A] 6.4 × 10-36 kgms-1
[B] 3.3 × 10-24 kgms-1
[C] 3.3 × 10-34 kgms-1

[D] none of these
Answer: 3.3 × 10-24 kgms-1
(13) In Thomson’s experiment number of parabola gives :
[A] the no. of electrons present in element
[B] the no. of proton present in element
[C] the no. of neutrons present in element
[D] the no. of isotopes of the element present
Answer: the no. of isotopes of the element present
(14) De-Broglie equation states the:
[A] dual nature
[B] particle nature
[C] wave nature
[D] None of these
Answer: dual nature
(15) The strength of photoelectric current depends upon :
[A] angle of incident radiation
[B] frequency of incident radiation
[C] intensity of incident radiation
[D] distance between anode and cathode
Answer: frequency of incident radiation
(16) What is the de-Broglie wavelength of a proton accelerated from rest through a potential difference of V volts?
[A]
[B]
[C]
[D] None of these
Answer: None of these
(17) In Davisson – Germer experiment, if the angle of diffraction is 52o, then the glancing angle will be:
[A] 32°
[B] 64°
[C] 72°
[D] 92°
Answer: 64°
(18) In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
[A] increasing the potential different between the anode and filament
[B] increasing the filament current
[C] decreasing the filament current
[D] decreasing the potential difference between the anode and filament
Answer: decreasing the potential difference between the anode and filament
(19) The energy of photon is equal to the K.E. of a proton. The energy of the photon is E. Let λ1  be the de- Broglie wavelength of the proton and  be the wavelength of the photon. The ratio λ1/ λ2 is proportional to
[A] Eo
[B] E1/2
[C] E-1
[D] E-1/2
Answer: E1/2
(20) The ratio of momenta of an electron and an alpha particle which are accelerated from rest through a potential different of 100 volt is
[A] 1:1
[B]
[C]
[D]
Answer: D

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