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Question
Assertion A: The photoelectric effect does not takes place, if the energy of the incident radiation is less than the work function of a metal.
Reason R: Kinetic energy of the photoelectrons is zero, if the energy of the incident radiation is equal to the work function of a metal.
Options
Both A and R are correct and R is the correct explanation of A.
Both A and R are correct but R is not the correct explanation of A.
A is correct but R is not correct.
A is not correct but R is correct.
Solution
Both A and R are correct but R is not the correct explanation of A.
Explanation: Electrons from metal surfaces are only ejected in the photoelectric effect when:
The incident photon's energy is larger than or equal to the metallic surface's work function.
Work function is the amount of energy needed to dislodge an electron from a metal surface.
∴ No electron will get free and the photoelectric effect will not occur when the photon's energy is lower than the work function.
Thus, Assertion (A) is correct.
By equation of photoelectric effect
hv = Φ + K.Emax
As per Reason (R), if K.E = 0
Then hv = Φ
Thus, Reason (R) is also correct
Therefore, Reason (R) does not support Assertion (A) because it does not take into account or provide an explanation for why the photoelectric effect would not occur if hn < Φ.
