physics : class12 Photoelectric Effect Laws : Particle Nature of Light : Dual Nature of Matter and Radiation MCQ Questions and Answers
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Photoelectric Effect Laws
MCQ questions and answers.
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MCQ Questions
1. What happens when the frequency of incident light is below the threshold frequency of a metal?
A.
Photoelectrons are emitted with low kinetic energy
B.
Photoelectrons are emitted after a time delay
C.
No photoelectrons are emitted
D.
The saturation current increases
Correct Answer:
No photoelectrons are emitted
Explanation:
According to the laws of the photoelectric effect, photoemission occurs only when the frequency of incident light is equal to or greater than the threshold frequency of the metal.
2. For light of frequency greater than the threshold frequency, photoelectric emission starts:
A.
After several seconds
B.
Instantaneously
C.
Only after heating the metal
D.
After increasing the intensity gradually
Correct Answer:
Instantaneously
Explanation:
One law of the photoelectric effect states that photoelectrons are emitted instantaneously when suitable light falls on the metal surface.
3. If the intensity of incident light is increased while its frequency remains constant and above the threshold frequency, the photoelectric current:
A.
Decreases
B.
Remains zero
C.
Increases
D.
Becomes independent of intensity
Correct Answer:
Increases
Explanation:
At a fixed frequency above the threshold value, increasing light intensity increases the number of emitted photoelectrons per second, so the photoelectric current increases.
4. The maximum kinetic energy of photoelectrons primarily depends on the:
A.
Intensity of incident light
B.
Frequency of incident light
C.
Area of the metal plate
D.
Duration of illumination
Correct Answer:
Frequency of incident light
Explanation:
The maximum kinetic energy of photoelectrons increases with the frequency of incident light and is not determined by its intensity.
5. If the intensity of light is increased without changing its frequency, the maximum kinetic energy of photoelectrons:
A.
Increases
B.
Decreases
C.
Remains unchanged
D.
Becomes zero
Correct Answer:
Remains unchanged
Explanation:
For a fixed frequency, changing the intensity changes the number of emitted electrons but does not change their maximum kinetic energy.
6. The stopping potential in a photoelectric experiment is independent of the:
A.
Frequency of light
B.
Work function of the metal
C.
Intensity of light
D.
Maximum kinetic energy of photoelectrons
Correct Answer:
Intensity of light
Explanation:
The stopping potential is related to the maximum kinetic energy of photoelectrons, which depends on frequency and the metal, but not on light intensity.
7. The saturation current in the photoelectric effect is mainly determined by the:
A.
Intensity of incident light
B.
Threshold frequency alone
C.
Stopping potential alone
D.
Colour of the metal surface alone
Correct Answer:
Intensity of incident light
Explanation:
Saturation current depends on the number of photoelectrons emitted per second, which increases with the intensity of incident light.
8. The minimum frequency needed to cause photoelectric emission from a metal is called:
A.
Resonant frequency
B.
Threshold frequency
C.
Stopping frequency
D.
Saturation frequency
Correct Answer:
Threshold frequency
Explanation:
Threshold frequency is the minimum frequency of incident radiation required to eject photoelectrons from a particular metal surface.
9. For a given metal, increasing the frequency of incident light above the threshold frequency causes the stopping potential to:
A.
Increase
B.
Decrease to zero
C.
Remain unchanged always
D.
Become independent of frequency
Correct Answer:
Increase
Explanation:
A higher light frequency gives photoelectrons greater maximum kinetic energy, so a larger stopping potential is required to stop them.
10. Which statement correctly describes the effect of increasing light intensity above the threshold frequency?
A.
It increases the number of emitted photoelectrons
B.
It lowers the threshold frequency of the metal
C.
It increases the work function of the metal
D.
It removes the instantaneous nature of emission
Correct Answer:
It increases the number of emitted photoelectrons
Explanation:
Increasing intensity means more photons strike the surface per second, causing more photoelectrons to be emitted and increasing the photoelectric current.
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Photoelectric Effect Laws
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