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

Question : A strong argument for the particle nature of cathode rays is that they
(a) produce fluoroscence
(b) travel through vacuum
(c) get deflected by electric and magnetic fields
(d) cast shadow

Answer: C

Question : In an electron gun the control grid is given a negative potential relative to cathode in order to
(a) decelerate electrons
(b) repel electrons and thus to control the number of electrons passing through it
(c) to select electrons of same velocity and to converge them along the axis.
(d) to decrease the kinetic energy of electrons

Answer: B

Question : When the speed of electrons increase, then the value of its specific charge
(a) increases
(b) decreases
(c) ramains unchanged
(d) increases upto some velocity

Answer: B

Question : Photoelectric effect is the phenomenon in which
(a) photons come out of a metal when it is hit by a beam of electrons.
(b) photons come out of the nucleus of an atom under the action of an electric field.
(c) electrons come out of a metal with a constant velocity
(d) which depends on the frequency and intensity of incident light wave.

Answer: D

Question : The photoelectrons emitted from a metal surface are such that their velocity
(a) is zero for all
(b) is same for all
(c) lies between zero and infinity
(d) lies between zero and a finite maximum

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

Answer: D

Question : When light is incident on a metal surface the maximum kinetic energy of emitted electrons
(a) vary with intensity of light
(b) vary with frequency of light
(c) vary with speed of light
(d) vary irregularly

Answer: B

Question : A photoelectric cell is a device which
(a) converts light into electricity
(b) converts electricity into light
(c) stores light
(d) stores electricity

Answer: A

Question : The maximum energy of electrons released in a photocell is independent of
(a) the frequency of the incident light
(b) the intensity of the incident light
(c) the nature of the cathode
(d) All of the above

Answer: C 

Question: Sodium and copper have work functions 2.3 eV and 4.5 eV respectively. Then the ratio of the wavelengths is nearest to
(a) 1 : 2
(b) 4 : 1
(c) 2 : 1
(d) 1 : 4

Answer: C

Question: The work functions of Silver and Sodium are 4.6 and 2.3 eV, respectively. The ratio of the slope of the stopping potential versus frequency plot for Silver to that of Sodium is
(a) 1
(b) 2
(c) 4
(d) zero

Answer: A

Question: In a photoelectric experiment the stopping potential for the incident light of wavelength 4000Å is 2 volt. If the wavelength be changed to 3000 Å, the stopping potential will be
(a) 2 V
(b) zero
(c) less than 2 V
(d) more than 2 V

Answer: D

Question: A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 2 m away, the number of electrons emitted by photocathode are reduced by a factor of
(a) 1/8
(b) 1/16
(c) 1/2
(d) 1/4

Answer: D

Question: Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell, the work function of the cathode surface is 4.2 eV. In order to reduce the photocurrent to zero the voltage of the anode relative to the cathode must be made
(a) – 4.2 V
(b) – 9.4 V
(c) – 17.8 V
(d) + 9.4 V

Answer: B

Question: In Davison-Germer experiment, an electron beam is incident on a crystal. The reflected beam consists of
(a) photons
(b) protons
(c) x-rays
(d) electrons

Answer: D

Question: In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
(a) increasing the potential difference 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: A

Question: Radiations of two photon’s energy, twice and ten times the work function of metal are incident on the metal surface successsively. The ratio of maximum velocities of photoelectrons emitted in two cases is
(a) 1 : 2
(b) 1 : 3
(c) 1 : 4
(d) 1 : 1

Answer: B

Question: When the minimum wavelength of X-rays is 2Å then the applied potential difference between cathode and anticathode will be
(a) 6.2 kV
(b) 2.48 kV
(c) 24.8 kV
(d) 62 kV

Answer: A

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