JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Critical Thinking

  • question_answer
    In the following arrangement y = 1.0 mm, d= 0.24 mm and D = 1.2 m. The work function of the material of the emitter is 2.2 eV. The stopping potential V needed to stop the photo current will be

    A)            0.9 V                                        

    B)            0.5 V

    C)            0.4 V                                        

    D)            0.1 V

    Correct Answer: A

    Solution :

                       As we know in Young's double slit experiment fringe width = separation between two consecutive fringe or dark fringes \[=\beta =\frac{\lambda D}{d}\] Here \[\beta =2y\] Þ \[2y=\frac{\lambda D}{d}\] Þ \[\lambda =\frac{2yd}{D}\] Þ \[\lambda =\frac{2\times 1\times {{10}^{-3}}\times 0.24\times {{10}^{-3}}}{1.2}=4\times {{10}^{-7}}m=4000\,{\AA}\] Energy of light incident on photo plate     \[E\,(eV)=\frac{12375}{4000}=3.1\,eV\] According to Eienstein photoelectric equation E = W0 + eV0  Þ \[{{V}_{0}}=\frac{(E-{{W}_{0}})}{e}=\frac{(3+2.2)}{e}eV\,\approx 0.9\,V\]


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