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NEET Sample Paper NEET Sample Test Paper-55

  • question_answer
    If stopping  potentials  corresponding to wavelengths \[4000\,\overset{{}^\circ }{\mathop{A}}\,\] and  \[4500\,\overset{{}^\circ }{\mathop{A}}\,\] are 1.3 V and 0.9 V, respectively, then the work function of the metal is-

    A) 0.3 eV              

    B) 1.3 eV

    C) 2.3 eV              

    D) 5 eV

    Correct Answer: C

    Solution :

    \[e\,{{V}_{sp}}\,=\,\frac{hc}{\lambda }\,\,-\,\,\phi \,\,\Rightarrow \,\,e{{V}_{sp}}\,+\,\phi \,\,=\,\,\frac{hc}{\lambda }\,\] \[1.3\,\,+\,\,\phi \,\,=\,\,\frac{hc}{4000}\] \[0.9\,\,+\,\,\phi \,\,=\,\,\frac{hc}{4500}\] \[\Rightarrow \,\,\,\frac{1.3+\phi }{0.9+\phi }\,\,=\,\,\frac{4500}{4000}\,\,=\,\,\frac{9}{8}\] \[10.4\,\,+\,\,8\phi \,\,=\,\,8.1\,\,+\,\,9\phi \] \[\Rightarrow \,\,\phi \,\,=\,\,2.3\text{ }eV\]


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