JEE Main & Advanced Chemistry Structure of Atom / परमाणु संरचना Sample Paper Topic Test - Structure of Atom

  • question_answer
    Photoelectric emission is observed from a surface for frequencies \[{{v}_{1}}\] and \[{{v}_{2}}\] of the incident radiation\[({{v}_{1}}-{{v}_{2}})\]. If the maximum kinetic energies of the photoelectrons in the two cases are in the ratio 1: k then the threshold frequency \[{{v}_{0}}\] is given by

    A) \[\frac{{{v}_{2}}-{{v}_{1}}}{k-1}\]

    B) \[\frac{k{{v}_{1}}-{{v}_{2}}}{k-1}\]

    C) \[\frac{k{{v}_{2}}-{{v}_{1}}}{k-1}\]

    D)  \[\frac{{{v}_{2}}-{{v}_{1}}}{k}\]

    Correct Answer: B

    Solution :

    [b] When frequency is \[{{v}_{1}}\],
    \[h{{v}_{1}}=h{{v}_{0}}+\frac{1}{2}mu_{1}^{2}\] ...(i)
    When frequency is \[{{v}_{2}}\],
    \[h{{v}_{2}}=h{{v}_{0}}+\frac{1}{2}mu_{2}^{2}\] ...(ii)
    \[\because \]       \[\frac{1}{2}mu_{1}^{2}-\frac{1}{k}\left( \frac{1}{2}mu_{2}^{2} \right)\]
    \[\therefore \]      from Eq. (i)
    \[h{{v}_{1}}=h{{v}_{0}}+\frac{1}{2k}mu_{2}^{2}\] ...(iii)
    or         \[\frac{1}{2}mu_{2}^{2}=kh{{v}_{1}}-kh{{v}_{0}}\] ...(iv)
    From Eqs. (ii) and (iv)
    \[h{{v}_{2}}=h{{v}_{0}}+kh{{v}_{1}}-kh{{v}_{0}}\]
    or         \[{{v}_{0}}(1-k)=v{{  }_{2}}-k{{v}_{1}}\]
    or         \[{{v}_{0}}=\frac{k{{v}_{1}}-{{v}_{2}}}{k-1}\]


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