NEET Sample Paper NEET Sample Test Paper-19

  • question_answer The threshold frequency for a certain photosensitive metal is \[{{V}_{0}}.\]When it is illuminated by light of frequency \[v=2{{V}_{0}},\]the maximum velocity of photoelectrons is \[{{\upsilon }_{0}}.\]What will be the maximum velocity of the photoelectrons when the same metal is illuminated by light of frequency\[v=5{{v}_{0}}?\]

    A) \[\sqrt{2}{{v}_{0}}\]            

    B) \[2{{v}_{0}}\]

    C) \[2\sqrt{2}{{v}_{0}}\]                      

    D) \[4{{v}_{0}}\]   

    Correct Answer: C

    Solution :

    \[\frac{1}{2}mu_{\max }^{2}=h(v-{{v}_{o}})\] For light of frequency \[v=2{{v}_{0}},\frac{1}{2}mu_{o}^{2}=h(2{{v}_{o}}-{{v}_{o}})=h{{v}_{o}}\] For light of frequency, \[v=5{{v}_{o}},\]we have \[\frac{1}{2}m{{u}^{2}}=h(5{{v}_{o}}-{{v}_{o}})=4\,h{{v}_{o}}\] \[\therefore \]\[{{u}^{2}}=4u_{o}^{2}\]or \[u=2{{u}_{o}}\] Hence, the correction option is [b].

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