Haryana PMT Haryana PMT Solved Paper-2000

  • question_answer
    The distance between two coherent sours is 1 mm. The screen is placed at a distance of 1 m from the source. If the distance of third bright fringe is 1.2 mm from the central fringe. The wavelength of light used is :

    A) \[7200\overset{\text{o}}{\mathop{\text{A}}}\,\]

    B) \[6800\overset{\text{o}}{\mathop{\text{A}}}\,\]

    C) \[5500\overset{\text{o}}{\mathop{\text{A}}}\,\]

    D) \[4000\overset{\text{o}}{\mathop{\text{A}}}\,\]

    Correct Answer: D

    Solution :

                    Here,  \[n=3,\,{{y}_{n}}=1.2mm=1.2\times {{10}^{-3}}m\] \[D=1m,\,d=1\times {{10}^{-3}}m\] For the position of maxima                       \[{{y}_{n}}=\frac{nD\lambda }{d}\] or            \[\lambda =\frac{{{y}_{n}}d}{nD}\]         So, the wavelength is given by                          \[\lambda =\frac{{{y}_{n}}d}{nD}=\frac{1.2\times {{10}^{-3}}\times 1\times {{10}^{-3}}}{3\times 1}\] or \[\lambda =0.4\times {{10}^{-6}}m=4\times {{10}^{-7}}m=4000\overset{\text{o}}{\mathop{\text{A}}}\,\] 


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