NEET AIPMT SOLVED PAPER SCREENING 2005

  • question_answer
                    The work functions for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einstein's equation, the metals which will emit photoelectrons for a radiation of wavelength \[4100\overset{\text{o}}{\mathop{\text{A}}}\,\] is/are:

    A)                                                                                                                                                                                            none   

    B)                 A only  

    C)                 A and B only

    D)                 all the three metals

    Correct Answer: C

    Solution :

                           Key Idea: That metal will emit photoelectrons which has work function lower than that obtained with the radiation of \[4100\overset{\text{o}}{\mathop{\text{A}}}\,\].                 Work function for wavelength of \[4100\overset{\text{o}}{\mathop{\text{A}}}\,\] is                 \[W=\frac{hc}{\lambda }\]                 \[=\frac{6.62\times {{10}^{-34}}\times 3\times {{10}^{8}}}{4100\times {{10}^{-10}}}\]                 \[=4.8\times {{10}^{-19}}J\]                 \[=\frac{4.8\times {{10}^{-19}}}{1.6\times {{10}^{-19}}}eV=3\,eV\]                 Now, we have                 \[{{W}_{A}}=1.92\,eV,\]                 \[{{W}_{B}}=2.0\,eV,\]                 \[{{W}_{C}}=5\,eV\]                 Since, \[{{W}_{A}}<W\]                 and \[{{W}_{b}}<W\], hence, A and B will emit photoelectrons.


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