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J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    The distance for which ray optics is good approximation for an aperture \[5\,\,mm\]and wavelength \[5000\overset{\text{o}}{\mathop{\text{A}}}\,\]is

    A)  \[18\,m\]            

    B)  \[30\,\,m\]

    C)  \[38\,\,m\]            

    D)  \[50\,\,m\]

    Correct Answer: D

    Solution :

    \[{{Z}_{F}}=\frac{{{a}^{2}}}{\lambda }\] \[{{Z}_{F}}\to \] Fresnel distance \[{{Z}_{F}}\simeq \frac{{{(5\times {{10}^{-3}})}^{2}}}{5000\times {{10}^{-10}}}=\frac{25\times {{10}^{-6}}}{5\times {{10}^{-7}}}=50\]m


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