Physics MCQs for Class 12 with Answers Chapter 11 Dual Nature of Matter and Radiation

Q.1. Cathode ray consists of
(a) photons
(b) electrons
(c) protons
(d) α-particles

Answer

Answer: (b) Cathode ray consists of electrons

Q.2. A discharge takes place between the two electrodes on applying the electric field to the gas in the discharge tube. The cause of this fluorescence was attributed to
(a) the radiations which appeared to be coming from the anode
(b) the radiation which appeared to be coming from the cathode
(c) the protons coming from the cathode
(d) the protons coming from the anode

Answer

Answer: (b) The fluorescence was caused due to the radiations appeared to be coming from the cathode called cathode rays.

Q.3. The presently accepted value of charge/mass (e/m) is
(a) 1.66 x 10^–19 c/kg
(b) 9.1 x 10¹¹ c/kg
(c) 1.76 x 10¹¹ c/kg
(d) 9.1 x 10¹⁹ c/kg

Answer

Answer: (c)

Q.4. 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

Answer: (b)

Q.5. Photoelectric emission occurs only when the incident light has more than a certain minimum
(a) power
(b) wavelength
(c) intensity
(d) frequency

Answer

Answer: (d)

Q.6. Which of the following when falls on a metal will emit photoelectrons ?
(a) UV radiations
(b) Infrared radiation
(c ) Radio waves
(d) Microwaves

Answer

Answer: (a) Emission of electron from a substance under the action of light is photoelectric effect. Light must be at a sufficiently high frequency. It may be visible light, U.V, X-rays. So U.V. cause electron emission.

Q.7. Particle like behavior of light arises from the fact that each quanta of light has definite …X… and a fixed value of …Y.. just like a particle, Here, X and Y refer to
(a) frequency, energy
(b) shape, volume
(c) energy, frequency
(d) energy, momentum

Answer

Answer: (d) Einstein arrived at the important result that the light quantum can also be associated with momentum hv/c A definite value of energy as well as momentum is a strong sign that the light quantum can be associated with a particle. This particle was later named photon.

Q.8. The wave nature of light was established by (i) Maxwell’s equations (ii) Fraunhoffer’s lines (iii) Hertz experiment (iv) Einstein’s theory
(a) (i) and (ii) only
(b) (ii) and (iv) only
(c) (i) and (iii) only
(d) (iii) and (iv) only

Answer

Answer: (c) The Maxwell’s equations of electromagnetism and Hertz experiment on the generation and detection of electromagnetic waves in 1887, strongly established the wave nature of light.

Q.9. The work-function of a metal is
(a) the minimum current required to take out electron from the metal surface
(b) the maximum frequency required to take out electron from the metal surface
(c) the minimum amount of energy required to take out the electron from the metal surface
(d) None of these

Answer

Answer: (c) A certain minimum amount of energy is required to pull the electron out from the surface of the metal. This minimum energy required by an electron to escape from the metal surface is called the work function of the metal.

Q.10. The work function of a metal is independent of
(i) nature of the surface of the metal
(ii) dimensions of the metal
(iii) properties of the metal
(iv) abundance of the metal
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)

Answer

Answer: (d) The work function of a metal depends upon the properties of the metal and the nature of its surface.

Q.11. The theory of quantisation of electric charge was given by
(a) William Crookes
(b) J. J. Thomson
(c) R.A. Millikan
(d) Wilhelm Hallwachs

Answer

Answer: (c) R.A. Millikan’s famous oil-drop experiment led him to propose the theory of quantisation of electric charge.

Q.12. In photoelectric effect, electrons are ejected from metals, if the incident light has a certain minimum
(a) wavelength
(b) frequency
(c) amplitude
(d) angle of incidence

Answer

Answer: (b) The minimum frequency above which the electrons are ejected from the metal surface, is called the threshold frequency for that metal. No electrons are emitted if the frequency of the incident light is less than the threshold frequency.

Q.13. Which of the following metals is not sensitive to visible light?
(a) Caesium
(b) Sodium
(c) Rubidium
(d) Cadmium

Answer

Answer: (d) Cadmium is sensitive to ultraviolet light while the rest are sensitive even to visible light.

Q.14. A photosensitive substance emits _____when illuminated by light.
(a) only protons
(b) only neutrons
(c) electrons and protons
(d) only electrons

Answer

Answer: (d) All photosensitive substances emit electrons when illuminated by light.

Q.15. The photoelectric current does not depend upon the
(i) frequency of incident light
(ii) work function of the metal
(iii) stopping potential
(iv) intensity of incident light
(a) (i) and (iv) only
(b) (ii) and (iii) only
(c) (iii) only
(d) (ii) only

Answer

Answer: (c) Beyond the threshold frequency the photoelectric current increases with increase in intensity.

Q.16. The stopping potential is directly related to
(a) the work function of the metal
(b) intensity of incident radiation
(c) the saturation current for the given frequency
(d) the kinetic energy gained by the photoelectrons

Answer

Answer: (d)

Q.17. The wave theory of light does not explain
(a) polarisation
(b) diffraction
(c) photocurrent
(d) interference

Answer

Answer: (c) Photocurrent can be explained with particle nature of light.

Q.18. Photoelectric effect can be explained by
(a) wave theory of light
(b) Bohr’s theory
(c) quantum theory of light
(d) corpuscular theory of light

Answer

Answer: (d) Photocurrent can be explained with particle nature of light.

Q.19. In Einstein’s picture of Photoelectric emission, the photoelectric emission does not take place by
(a) continuous emission of energy from radiation
(b) continuous absorption of energy from radiation
(c) discrete absorption of energy from radiation
(d) discrete emission of energy from radiation

Answer

Answer: (b) The photoelectric emission takes place by discrete absorption of energy from radiation.

Q.20. The particle nature of light is not confirmed by
(a) photoelectric effect
(b) scattering of X-rays by electrons
(c) diffraction of electrons
(d) compton effect

Answer

Answer: (c) The diffraction of electrons show wave nature of electrons.

Q.21. Photons are deflected by
(a) electric field only
(b) magnetic field only
(c) electromagnetic field
(d) None of these

Answer

Answer: (d) Photons are not deflected by electric and magnetic fields as they are electrically neutral.

Q.22. Electrically, photons are
(a) positively charged
(b) negatively charged
(c) neutral
(d) strongly charged, may be positive or negative

Answer

Answer: (c) Photons are quantum of light which are electrically neutral.

Q.23. In a photon-particle collision, the quantity that does not remain conserved is
(a) total energy
(b) total momentum
(c) number of photons
(d) None of these

Answer

Answer: (c) In a photon – particle collision, the number of photons may not be conserved. The photon may be absorbed or a new photon may be created.

Q.24. Of the following properties, the photon does not possess
(a) rest mass
(b) momentum
(c) energy
(d) frequency

Answer

Answer: (a) Photon has no rest mass.

Q.25. It is essential to consider light as a stream of photons to explain
(a) diffraction of light
(b) refraction of light
(c) photoelectric effect
(d) reflection of light

Answer

Answer: (c) Photoelectric effect can be explained by quantum nature of light i.e. light as a stream of photons.

Q,26. Photoelectric effect was discovered by
(a) Hertz
(b) Hallwachs
(c) Lenard
(d) Millikan

Answer

Answer: (a) Hertz discovered first the photoelectric effect in 1887.

Q.27. The momentum of a photon of wavelength λ is
(a) hλ
(b) h/λ
(c) λ/h
(d) h/cλ

Answer

Answer: (b)

Q.28. The photo-electrons 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

Answer: (d)

Q.29. Photoelectric effect shows
(a) wave like behaviour of light
(b) paritcle like behaviour of light
(c) both wavelike and paticle like behaviour
(d) neither wave like nor particle like behaviour of light

Answer

Answer: (b) Photoelectric effect is accounted by particle like bahaviour of light (i.e. by quantum theory of light)

Q.30. A photoelectric cell converts
(a) light energy into heat energy
(b) light energy to sound energy
(c) light energy into electric energy
(d) electric energy into light energy

Answer

Answer: (c) Photoelectric cell converts light energy into electric energy.

Q.31. Light of a particular frequency 􀁑 is incident on a metal surface. When the intensity of incident radiation is increased, the photoelectric current
(a) decreases
(b) increases
(c) remains unchanged
(d) sometimes increases and sometimes decreases

Answer

Answer: (b) The photoelectric current α Intensity of light.

Q.32. The photoelectric effect is based on the law of conservation of
(a) momentum
(b) energy
(c) angular momentum
(d) mass

Answer

Answer: (b) Photoelectric effect is based on law of conservation of energy.

Q.33. The photoelectric effect can be understood on the basis of
(a) wave theroy of light only
(b) electromagnetic theory of light only
(c) quantum theory of light only
(d) None of these

Answer

Answer: (c)

Q.34. 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

Answer: (b)

Q.35. 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

Answer: (c) Max. K.E. of phtoelectrons emitted is independent of intensity of incident light.

Q.36. Einstein’s photoelectric equation states that
hν = W₀ + E_k.
In this equatin, E_k refers to the
(a) kinetic energy of all the emitted electrons
(b) mean kinetic energy of the emitted electrons
(c) maximum kinetic energy of the emitted electrons
(d) minimum kinetic energy of the emitted electrons

Answer

Answer: (c) In the given relation E_k stands for maximum K.E. of emitted photoelectrons.

Q.37. In the photoeletric effect, electrons are emitted
(a) at a rate that is proportional to the amplitude of the incident radiation
(b) with a maximum velocity proportional to the frequency of the incident radiation
(c) at a rate that is independent of the emitter
(d) only if the frequency of the incident radiations is above a certain threshold value

Answer

Answer: (d) Photoelectrons are emitted if the frequency of incident light is greater than the threshold frequency.

Q.38. The minimum energy required to eject an electron, from the metal surface is called
(a) atomic energy
(b) mechanical energy
(c) electrical energy
(d) work function

Answer

Answer: (d) The minimum energy required for the emission of electrons is called work function.

Q.39. The work function for photoelectric effect
(a) is different for different metals
(b) is same for all metals
(c) depends upon the intensity of incident light
(d) depends upon the frequency of incident light

Answer

Answer: (a) The work function of different metals is different.

Q.40. 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

Answer: (d) The work function of different metals is different.

Q.41. A photoelectric cell is a device which
(a) converts light into electricity
(b) converts electricity into light
(c) stores light
(d) stores electricity

Answer

Answer: (a)

Q.42. Which of the following shows particle nature of light?
(a) Refraction
(b) Interference
(c) Polarization
(d) Photoelectric effect

Answer

Answer: (d)

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