JEE Main & Advanced Sample Paper JEE Main - Mock Test - 9

  • question_answer
    In a diffraction pattern due to a single slit of width 'a', the first minimum is observed at an angle \[30{}^\circ \] when light of wavelength \[5000\overset{o}{\mathop{A}}\,\]is incident on the slit. The first secondary maximum is observed at an angle of:

    A) \[{{\sin }^{-1}}\left( \frac{1}{4} \right)\]           

    B) \[{{\sin }^{-1}}\left( \frac{2}{3} \right)\]

    C) \[{{\sin }^{-1}}\left( \frac{1}{2} \right)\]

    D) \[{{\sin }^{-1}}\left( \frac{3}{4} \right)\]

    Correct Answer: D

    Solution :

    For the first minima, \[\theta =\frac{\eta \lambda }{a}\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\,\,\sin 30{}^\circ =\frac{\lambda }{a}=\frac{1}{2}\] First secondary maxima will be at, \[\sin \theta =\frac{3\lambda }{2a}=\frac{3}{2}\left( \frac{1}{2} \right)\,\,\,\,\,\,\,\,\,\,\,\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\theta ={{\sin }^{-1}}\left( \frac{3}{4} \right)\]


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