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Structure of Atom question

2023 · 11 Apr · Shift 1 · Q4
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Structure of Atom question

2023 · 11 Apr · Shift 1 · Q4

JEE MainChemistryStructure of AtomMCQ+4 / −1
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R : Assertion A : In the photoelectric effect, the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface. Reason R : When the photon of any energy strikes an electron in the atom, transfer of energy from the photon to the electron takes place. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Both A and R are correct and R is the correct explanation of A
  2. B
    A is not correct but R is correct
  3. C
    A is correct but R is not correct
  4. D
    Both A and R are correct but R is NOT the correct explanation of A
View written solutionFree

Correct answer: C

  1. Analyze Assertion A

    Assertion A says: In the photoelectric effect, the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface.

    This is correct.

    In photoelectric effect, if the incident light has frequency ν>ν0\nu > \nu_0ν>ν0​ (threshold frequency), then each photon has energy E=hνE = h\nuE=hν which is sufficient to overcome the work function ϕ=hν0.\phi = h\nu_0.ϕ=hν0​. Hence emission occurs instantaneously, i.e. without measurable time lag.

  2. Analyze Reason R

    Reason R says: When the photon of any energy strikes an electron in the atom, transfer of energy from the photon to the electron takes place.

    This is not correct.

    Energy transfer from a photon to an electron is not guaranteed for any energy. In atomic systems, absorption occurs only when the photon energy matches the allowed energy difference between two levels: hν=ΔE.h\nu = \Delta E.hν=ΔE. So a photon of arbitrary energy is not necessarily absorbed by an electron.

    Also, in photoelectric effect, emission occurs when photon energy is at least equal to the work function: hν≥ϕ.h\nu \ge \phi.hν≥ϕ. Thus the statement "photon of any energy" is false.

  3. Conclusion

    • Assertion A is correct.
    • Reason R is incorrect.

    Therefore, the correct option is: C\boxed{\text{C}}C​

  4. Comparison with stored answer

    Stored correct answer: C

    My derived answer: C

    Hence, they agree.

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