Free Dawn of Modern Physics MCQs with Answers
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Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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Read the Dawn of Modern Physics notesFree MDCAT chapter notes with key terms739 questions · page 7 of 37
- A. the energy required to remove an electron from the sample
- B. the kinetic energy of the most energetic electron ejected
- C. the potential energy of the most energetic electron ejected
- D. the electric potential that causes the electron current to vanish
Explanation: The stopping potential is that retarding voltage for which the photoelectric current becomes zero. Even the electrons of maximum K.E.
Correct answer: the electric potential that causes the electron current to vanish- A. the energy of the least energetic electron before it is ejected
- B. the energy of the least energetic electron after it is ejected
- C. the energy of the most energetic electron before it is ejected
- D. the energy of the most energetic electron after it is ejected
Explanation: This fact shows that maximum K.E. of photoelectrons directly depends upon the frequency of light but independent of the intensity of light.
Correct answer: the energy of the most energetic electron after it is ejected- A. their kinetic energy
- B. the work function
- C. the number of photons that hit the sample
- D. the frequency of the incident light
Explanation: In photoelectric effect electrons are emitted instantaneously; the intensity (the number of Photons that hit the sample) of light…
Correct answer: the number of photons that hit the sample- A. frequency of the incident light
- B. intensity of the incident light
- C. time for which the light falls on the metal
- D. All of above
Explanation: In photoelectric effect electrons are emitted with different energies. The maximum energy of photoelectrons depends on the nature of metal…
Correct answer: frequency of the incident light- A. N ∝ L and E ∝ λ
- B. N ∝ L and E ∝ L
- C. N ∝ L and E ∝ 1/λ
- D. N ∝ 1/λ and E ∝ 1/L
Explanation: In photoelectric effect Electrons are emitted instantaneously; the intensity of light determines only their numbers.
Correct answer: N ∝ L and E ∝ 1/λ- A. intensity of light
- B. frequency of light
- C. work function of the metal
- D. Nature of material
Explanation: In photoelectric effect Electrons are emitted instantaneously; the intensity of light determines only their numbers. No.
Correct answer: intensity of light- A. kinetic energy
- B. potential energy
- C. binding energy
- D. thermal energy
Explanation: Energy of photon = work function + Max. K.E. of photoelectrons hf =Φ+ K.Emax
Correct answer: kinetic energy- A. directly proportional to
- B. inversely proportional to
- C. independent of
- D. directly proportional to square root of intensity
Explanation: Maximum K.E of photoelectrons ∝ Frequency of incident light
Correct answer: directly proportional to- A. minimum frequency
- B. angular frequency
- C. maximum frequency
- D. threshold frequency
Explanation: There is a minimum frequency below which no electrons are emitted however intense the light may be.
Correct answer: threshold frequency- A. Frequency of incident light
- B. nature of material
- C. Intensity of incident light
- D. Frequency of light and nature of material
Explanation: The threshold frequency depends upon the nature of the metal. It is different for different metals.
Correct answer: nature of material- A. The electrons coming out of the metal surface with minimum energy
- B. The electrons coming out of the metal surface with full surplus energy (without losing any energy during collisions with the atoms of metal)
- C. The photons of light that reflect back from the metal surface
- D. All the electrons that come out of the metal surface
Explanation: If the energy of the photon is greater than the work function, then a part of it is used in escaping an electron from the metal surface.
Correct answer: The electrons coming out of the metal surface with full surplus energy (without losing any energy during collisions with the atoms of metal)- A. photo-voltaic cell
- B. photo-cell
- C. photo-phone
- D. photo-door
Explanation: A photocell is a device which converts light energy into electrical energy. It works on the photoelectric effect.
Correct answer: photo-cell- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: Photo electric current does not depend upon frequency of photon.
Correct answer: Option A- A. Annihilation of matter
- B. Pair production
- C. Production of X-rays
- D. Nuclear fission
Explanation: The reverse process of the photoelectric effect is b) pair production. The photoelectric effect involves the emission of electrons from a…
Correct answer: Production of X-rays- A. The photoelectric current will decrease
- B. The photoelectric current will increase
- C. The stopping potential will decrease
- D. The stopping potential will increase
Explanation: The correct option is c) The stopping potential will increase if the wavelength of the incident radiation in a photoelectric experiment is…
Correct answer: The stopping potential will increase- A. The number of electrons emitted is a quarter of the initial number
- B. The number of electrons emittedis half the initial number
- C. Each electron emitted carries one quarter of initial energy
- D. Each emitted electron carries half the initial energy
Explanation: If distance from source becomes double then intensity of light and number of emitted electrons reduce to one fourth.
Correct answer: Each emitted electron carries half the initial energy- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: After the threshold frequency (K.E)e ∝ Frequency of incident light. The graph should be a straight line: In the photoelectric effect, the…
Correct answer: Option D- A. -2 V
- B. -4 V
- C. -3 V
- D. -1 V
Explanation: Stopping potential is that negative potential for which photo electric current is zero.
Correct answer: -4 V- A. The frequency of the incident light
- B. Their potential energy
- C. The number of photons that hit the sample
- D. Their kinetic energy
Explanation: No of electrons ejected ∝ intensity of light (No of photons)
Correct answer: The frequency of the incident light- A. The value of saturation current increases
- B. No effect
- C. The value of stopping potential increases
- D. The value of stopping potential decreases
Explanation: Please note that the correct option for the changes observed during Einstein's Photoelectric Experiment when the frequency of the incident…
Correct answer: The value of saturation current increases