Haryana PMT Haryana PMT Solved Paper-2008

  • question_answer
    When photons of energy hv fall on an    aluminium plate (of work function \[{{E}^{0}}\]),              photoelectrons of maximum kinetic energy K are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be

    A)  \[K+{{e}_{0}}\]                                

    B)  \[2K\]

    C)  \[K\]                                    

    D)  \[K+hv\]

    Correct Answer: D

    Solution :

                    According to Einsteins photoelectric effect energy of photon = KE of photoelectron \[+\] work function of metal ie,      \[hv=\frac{1}{2}m{{v}^{2}}+{{E}_{0}}\]                        or            \[hv={{K}_{\max }}+{{E}_{0}}\]              ?.(i) Now, we have given,  \[v=2v\] Therefore,  \[K{{}_{\max }}=2hv-{{E}_{0}}\] From Eqs. (i) and (ii) we have We have                 \[K{{}_{\max }}=2({{K}_{\max }}+{{E}_{0}})-{{E}_{0}}\]                 \[=2{{K}_{\max }}+{{E}_{0}}\]                 \[={{K}_{\max }}+({{K}_{\max }}+{{E}_{0}})\]                 \[={{K}_{\max }}+hv\]  [From Eq. (i)] putting \[{{K}_{\max }}=K\] \[\therefore \]  \[K{{}_{\max }}=K+hv\]


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