BHU PMT BHU PMT Solved Paper-2002

  • question_answer
    The fringe width for a source of light of wavelength 5000 \[\mathbf{B}\] in the Young's experiment, is 0.5 mm. If the source is replaced by another source of wavelength 6000 \[4\,\Omega \], keeping other  setting same, the fringe width will be :                                                                                                                                                    [BHU PMT-2002]

    A)                  \[6\,\Omega \]               

    B)                  \[3\,\Omega \]

    C)                  \[20\,\Omega \]                             

    D)                  \[3.33\times {{10}^{8}}\,m/s\]

    Correct Answer: A

    Solution :

                     In Young?s double slit experiment fringe width \[\left( W \right)\] is given by                 \[W=\frac{D\lambda }{d}\]                 Where \[D\] is the distance between the screen and source, d is distance between coherent sources and \[\lambda \] is wavelength of light employed.                 Given, \[{{\lambda }_{1}}=5000\,\overset{\circ }{\mathop{\text{A}}}\,,\,{{W}_{1}}=0.5\,mm\,\,{{\lambda }_{2}}=6000\overset{\circ }{\mathop{\text{A}}}\,.\]                                                 \[\frac{{{W}_{1}}}{{{W}_{2}}}=\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{5000}{6000}\]                 \[\Rightarrow \]                               \[\frac{0.5}{{{W}_{2}}}=\frac{5}{6}\]                 \[\Rightarrow \]                               \[{{W}_{2}}=\frac{3}{5}=0.6\,\,mm\]                 Note: Fringe width increases as wavelength of light increases.


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