JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Critical Thinking

  • question_answer
    The ratio of the intensity at the centre of a bright fringe to the intensity at a point one-quarter of the distance between two fringe from the centre is

    A)            2    

    B)            1/2

    C)            4    

    D)            16

    Correct Answer: A

    Solution :

               \[I=4{{I}_{0}}{{\cos }^{2}}\frac{\varphi }{2}\] At central position \[{{I}_{1}}=4{{I}_{0}}\]     ??(i) Since the phase difference between two successive fringes is \[2x,\] the phase difference between two points separated by a distance equal to one quarter of the distance between the two, successive fringes is equal to \[\delta =(2\pi )\,\left( \frac{1}{4} \right)=\frac{\pi }{2}\] radian \[\Rightarrow {{I}_{2}}=4{{I}_{0}}{{\cos }^{2}}\left( \frac{\frac{\pi }{2}}{2} \right)=2{{I}_{0}}\]         ??(ii) Using (i) and (ii),  \[\frac{{{I}_{1}}}{{{I}_{2}}}=\frac{4\,{{I}_{0}}}{2\,{{I}_{0}}}=2\]


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