JEE Main & Advanced JEE Main Paper (Held On 11 April 2015)

  • question_answer
    In a Young's double slit experiment with light of wavelength\[\lambda \]the separation of slits is d and distance of screen is D such that \[D>>d>>\lambda .\]If the Fringe width is \[\beta ,\] the distance from point of maximum intensity to the point where intensity falls to half of maximum intensity on either side is : [JEE Main Online Paper (Held On 11 April 2015)]  

    A) \[\frac{\beta }{2}\]

    B) \[\frac{\beta }{4}\]

    C) \[\frac{\beta }{3}\]

    D) \[\frac{\beta }{6}\]

    Correct Answer: B

    Solution :

      \[I=4{{I}_{0}}{{\cos }^{2}}\left( {}^{\phi }/{}_{2} \right)\] \[{{\operatorname{I}}_{max}}=4{{I}_{0}}\] Now\[\frac{{{\operatorname{I}}_{max}}}{2}=2{{I}_{0}}=4{{I}_{0}}{{\cos }^{2}}\left( {}^{\phi }/{}_{2} \right)\] \[\cos \left( {}^{\phi }/{}_{2} \right)=\frac{1}{\sqrt{2}}\] \[\therefore \]\[\frac{\phi }{2}=\frac{\pi }{2}\] \[\therefore \]\[\phi =\frac{\pi }{2}\] \[\frac{2\pi }{\lambda }\Delta x=\frac{\pi }{2}\] \[\therefore \]\[\Delta x=\frac{\pi }{4}\] \[y\frac{d}{D}=\frac{\lambda }{4}\] \[\therefore \]\[y=\frac{\lambda D}{4d}\] \[\therefore \]\[\]


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