NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    When the light of frequency \[2{{v}_{0}}\](where \[{{v}_{0}}\] is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is \[{{v}_{1}}\]. When the frequency of the incident radiation is increased to \[5{{v}_{0}}\], the maximum velocity of electrons emitted from the same plate is \[{{v}_{2}}\]. The ratio of \[{{v}_{1}}\] to \[{{v}_{2}}\] is                                                                                              [NEET - 2018]

    A)  \[4:1\]              

    B)       \[1:4\]

    C)  \[1:2\]              

    D)       \[2:1\]

    Correct Answer: C

    Solution :

    [c] \[\text{E=}{{\text{W}}_{\text{0}}}\text{+}\frac{\text{1}}{\text{2}}\text{m}{{\text{v}}^{\text{2}}}\]
    \[\text{h(2}{{\text{v}}_{\text{0}}}\text{)=h}{{\text{v}}_{\text{0}}}\text{+}\frac{\text{1}}{\text{2}}\text{mv}_{\text{1}}^{\text{2}}\]
    \[\text{h}{{\text{v}}_{\text{0}}}\text{=}\frac{\text{1}}{\text{2}}\text{mv}_{\text{1}}^{\text{2}}\]          …(i)
    \[\text{h(5}{{\text{v}}_{0}})=h{{v}_{0}}+\frac{1}{2}mv_{2}^{2}\]
    \[4h{{v}_{0}}=\frac{1}{2}mv_{2}^{2}\]                              …(ii)
    Divide (i) by (ii)
    \[\frac{1}{4}=\frac{v_{1}^{2}}{v_{2}^{2}}\]
    \[\frac{{{v}_{1}}}{{{v}_{2}}}=\frac{1}{2}\]


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