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Practice MCQ Question for Class 12 Physics chapter-wise

1. De-Broglie equation states the:

(a) dual nature
(b) particle nature
(c) wave nature
(d) none of these

2. 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

3. Kinetic energy of emitted electrons depends upon :

(a) frequency
(b) intensity
(c) nature of atmosphere surrounding the electrons
(d) none of these

4. 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

5. Millikan’s oil drop experiment makes use of:

(a) Stokes’ law
(b) Boyle’s law
(c) Gas equation
(d) Bernoulli’s theorem

6. When a yellow light is incident on a surface, no electrons are emitted while green light can emit electrons. If the red light is incident on the surface then:

(a) no electrons are emitted
(b) photons are emitted
(c) electrons of higher energy are emitted
(d) electrons of lower energy are emitted

7. Evidence of the wave nature of light cannot be obtained from:

(a) diffraction
(b) interference
(c) doppler effect
(d) reflection

8. According to Einstein’s photoelectric equation the plot of the kinetic energy of the emitted photo-electrons from a metal vs the frequency of the incident radiation gives a straight line whose slope

(a) depends on the nature of the metal used
(b) depends on the intensity of the radiation
(c) depends both on the intensity of the radiation and the metal used
(d) is the same for all metals and independent of the intensity of the radiation

9. A metal surface ejects electrons when hit by green light but nothing when hit by yellow light. The electrons will be ejected when the surface is hit by

(a) blue light
(b) heat rays
(c) infrared light
(d) red light

10. Which of the following statements is correct regarding the photoelectric experiment?

(a) The photocurrent increases with intensity of light
(b) Stopping potential increases with increase in intensity of incident light
(c) The photocurrent increases with increase in frequency
(d) All of these

11. Which phenomenon best supports the theory that matter has a wave nature?

(a) Electron momentum
(b) Electron diffraction
(c) Photon momentum
(d) Photon diffraction

12. 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

13. 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

14. 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

15. 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

16. Photoelectric emmision occurs only when the incident light has more than a certain minimum

(a) power
(b) wavelength
(c) intensity
(d) frequency

17. A photoelectric cell is a device which

(a) converts light into electricity
(b) converts electricity into light
(c) stores light
(d) stores electricity

18. Of the following properties, the photon does not possess

(a) rest mass 
(b) momentum
(c) energy 
(d) frequency

19. 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

20.  Electron volt (ev) is the unit of

(a) energy 
(b) potential
(c) current 
(d) charge

21. In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

(a) increasing the filament current
(b) decreasing the filament current
(c) decreasing the potential difference between the anode and filament
(d) increasing the potential difference  between the anode and filament

22.  A particle which has zero rest mass and non-zero energy and momentum must travel with a speed:

(a) Equal to c, the speed of light in vacuum
(b) Greater than c
(c) Less than c
(d) Tending to infinity

23. Photocell is a device to: 

(a) Store photons
(b) Measure light intensity
(c) Convert photon energy into mechanical energy
(d) Store electrical energy for replacing storage batteries

24. When ultraviolet radiation is incident on asurface, no photoelectrons are emitted. If asecond beam causes photoelectrons to beejected, it may consists of    

(a) infra-red waves
(b) X-rays
(c) visible light rays
(d) radio waves

25. 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 :

1. Answer : (a) dual nature

Explanation: De Broglie equation states that a matter can act as waves much like light and radiation, which also behave as waves and particles. The equation further explains that a beam of electrons can also be diffracted just like a beam of light.

2. Answer : (d) Momentum

Explanation: As \(\lambda\propto\frac{1}{p}\)∴ momentum is some for both

3. Answer : (a) frequency

Explanation: Thus the kinetic energy of the emitted photoelectrons depends on wavelength, frequency of the incident photon, and work function of the metal but does not depend on the intensity.

4. Answer : (c) intensity of incident radiation

Explanation: Current in a photoelectric effect is dependent on the intensity of the incident light because as the intensity of light increases, number of electrons ejected per second increases, so, current increases.

5. Answer : (a) Stokes’ law

Explanation: In Millikan's oil drop experiment, we make use of Stoke's law. In this experiment, charge on electron was determined to be −1.6×10^-19 C.

6. Answer : (a) no electrons are emitted

Explanation: λ_r > λ_y > λ_g. Here threshold wavelength <λ_y .hence, no electrons are emitted.

7. Answer : (d) reflection

Explanation: The wave nature of light can not be obtained from reflection of light.

8. Answer : (d) is the same for all metals and independent of the intensity of the radiation

Explanation: KE_max = hν − W_y = mx + C

9. Answer : (a) blue light

Explanation: The photoelectric emission is possible if the wavelength of the incident light is less than that of yellow light.

10. Answer : (a) The photocurrent increases with intensity of light

Explanation: The photocurrent increases linearly with intensity of the incident light, but is independent of its frequency The stopping potential increases linearly with the frequency of the incident light, but is independent of its intensity .

11. Answer : (b) Electron diffraction

Explanation: Electron diffraction is the diffraction of a beam of electrons by atoms or molecules. The fact that electrons can be diffracted in a similar way to light shows the particles can act as waves.

12. Answer : (c) get deflected by electric and magnetic fields

Explanation: A strong argument for the particle nature of cathode rays is they are deflected by electric and magnetic fields.

13. Answer : (b) repel electrons and thus to control the number of electrons passing through it

Explanation: In an electron gun the control grid is given a negative potential relative to cathode in order to repel electrons and thus to control the number of electrons passing through it.

14. Answer : (b) decreases

Explanation: When speed of electron increases the specific charger decreases because with increase in velocity charge remains constant. Another reason is specifice charge is the ratio of the charge to mass.

15. Answer : (b) X-rays emission

Explanation:  (i) Thermionic emission : When a metal is heated to a high temperature, the free electron gain kinetic energy and escape from the surface of the metal.

(ii) Secondary emission : When an electron strikes the surface of a metallic plate, it emits other electrons from the surface.

(iii) Photoelectric emission : Emission o felectrons from the metal surface on irradiation with radiation of suitable frequency

(iv) X-rays emission : They are due to transitions in the inner energy levels of the atom.

16. Answer : (d) frequency

Explanation: Photoelectron emission take place when certain minimum "frequency" light fall on metal surface.

17. Answer : (a) converts light into electricity

Explanation: Photoelectric cell or photocell, device whose electrical characteristics (e.g., current, voltage, or resistance) vary when light is incident upon it. The most common type consists of two electrodes separated by a light-sensitive semiconductor material. The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner can be called photoelectrons.

18. Answer : (a) rest mass 

Explanation: A particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass.

19. Answer : (d) work function

Explanation: Electrons ejected from a sodium metal surface were measured as an electric current. The minimum energy required to eject an electron from the surface is called the photoelectric work function.

20. Answer : (a) energy 

Explanation: The electronvolt (eV) is a unit of energy whereas the volt (V) is the derived SI unit of electric potential. The SI unit for energy is the joule (J).

21. Answer : (d) increasing the potential difference  between the anode and filament

Explanation: Velocity of electron emitted from the electron gun can be increased by potential difference between the anode and filament.

22. Answer : (a) Equal to c, the speed of light in vacuum

Explanation: Particle is photon and it travels with the velocity equal to light in vacuum.

23. Answer : (b) Measure light intensity

Explanation: Photocell is an optoelectronic device that works on the principle of photoelectric effect. It is mainly used to detect light of suitable wavelength.

24. Answer : (b) X-rays

Explanation: Energy of photon of X-rays is more than energy of photon of ultraviolet rays. Because frequency of X rays is more than ultraviolet rays.

25. Answer : (d) electrons

Explanation: The scattered beam consists of electrons.

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