JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Diffraction of Light

  • question_answer
    A plane wavefront \[(\lambda =6\times {{10}^{-7}}m)\] falls on a slit \[0.4\,mm\] wide. A convex lens of focal length \[0.8\,m\] placed behind the slit focusses the light on a screen. What is the linear diameter of second maximum                                                                             [RPMT 2001]

    A)            \[6\,mm\]                             

    B)            \[12\,mm\]

    C)            \[3\,mm\]                             

    D)            \[9\,mm\]

    Correct Answer: A

    Solution :

                       For secondary maxima \[d\sin \theta =\frac{5\lambda }{2}\] \[\Rightarrow d\theta \,=d.\frac{x}{D(\approx \,f)}=\frac{5\lambda }{2}\] \[\Rightarrow 2x=\frac{5\lambda f}{d}=\frac{5\times 0.8\times {{10}^{-7}}}{4\times {{10}^{-4}}}=6\times {{10}^{-3}}m=6mm\]


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