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Dual Nature of Radiation question

2010 · Shift 0 · Q55
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Dual Nature of Radiation question

2010 · Shift 0 · Q55

JEE MainPhysicsDual Nature of RadiationMCQ+4 / −1
Statement - 111: When ultraviolet light is incident on a photocell, its stopping potential is V0{V_0}V0​ and the maximum kinetic energy of the photoelectrons is Kmax⁡{K_{\max }}Kmax​. When the ultraviolet light is replaced by XXX-rays, both V0{V_0}V0​ and Kmax⁡{K_{\max }}Kmax​ increase. Statement -222 : Photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of frequencies present in the incident light.
  1. A
    Statement - 111 is true, Statement -222 is true; Statement -222 is the correct explanation of Statement -111
  2. B
    Statement - 111 is true, Statement -222 is true; Statement -222 is not the correct explanation of Statement -111
  3. C
    Statement - 111 is is false, Statement -222 is true
  4. D
    Statement - 111 is is true, Statement -222 is false
View written solutionFree

Correct answer: D

  1. Use Einstein’s photoelectric equation

    For photoelectric emission, Kmax⁡=hν−ϕK_{\max}=h\nu-\phiKmax​=hν−ϕ where ϕ\phiϕ is the work function of the metal.

    Also, stopping potential V0V_0V0​ is related to maximum kinetic energy by eV0=Kmax⁡eV_0=K_{\max}eV0​=Kmax​

  2. Check Statement-1

    If ultraviolet light is replaced by X-rays, then the frequency ν\nuν of incident radiation increases significantly.

    Since Kmax⁡=hν−ϕK_{\max}=h\nu-\phiKmax​=hν−ϕ a larger ν\nuν gives a larger Kmax⁡K_{\max}Kmax​.

    Then from eV0=Kmax⁡eV_0=K_{\max}eV0​=Kmax​ the stopping potential V0V_0V0​ also increases.

    Hence, Statement-1 is true.

  3. Check Statement-2

    Statement-2 says that photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of frequencies present in the incident light.

    This is not correct as a general explanation of the spread in electron speeds.

    Even if the incident light is monochromatic, emitted photoelectrons can still have kinetic energies ranging from nearly zero to Kmax⁡K_{\max}Kmax​. This happens because electrons originate from different depths and energy states inside the metal and may lose different amounts of energy before escaping.

    So the spread in speeds is not due to a range of frequencies in the incident light.

    Hence, Statement-2 is false.

  4. Choose the correct option

    • Statement-1: True
    • Statement-2: False

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

  5. Compare with stored answer

    The stored correct answer is B, but our derivation gives D.

    Therefore, I disagree with the stored answer. Statement-2 is false in standard photoelectric theory.

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