JEE Main & Advanced JEE Main Paper (Held On 09-Jan-2019 Morning)

  • question_answer
    Two coherent sources produce waves of different intensities which interfere. After interference, the ratio of the maximum intensity to the minimum intensity is 16. The intensity of the waves are in the ratio: [JEE Main Online Paper (Held On 09-Jan-2019 Morning]

    A) 25 : 9   

    B) 4 : 1

    C) 5 : 3             

    D) 16 : 9

    Correct Answer: A

    Solution :

    \[\frac{{{\operatorname{I}}_{max.}}}{{{\operatorname{I}}_{min.}}}\,\,=\,\,{{\left( \frac{\sqrt{{{I}_{1}}}+\sqrt{{{I}_{2}}}}{\sqrt{{{I}_{1}}}-\sqrt{{{I}_{2}}}} \right)}^{2}}\,\,\,=\,\,\,16\,\,\,=\,\,{{4}^{2}}\] \[\Rightarrow \,\,\,\,\frac{\sqrt{{{I}_{1}}}+\sqrt{{{I}_{2}}}}{\sqrt{{{I}_{1}}}-\sqrt{{{I}_{2}}}}\,\,\,=\,\,\,4\] \[\sqrt{{{I}_{1}}}+\sqrt{{{I}_{2}}\,}\,\,=\,\,4\sqrt{{{I}_{1}}}-\,\,4\sqrt{{{I}_{2}}}\] \[\Rightarrow \,\,\,5\sqrt{{{I}_{2}}}\,\,\,=\,\,\,3\sqrt{{{I}_{1}}}\] \[\frac{{{I}_{1}}}{{{I}_{2}}}\,\,=\,\,\frac{25}{9}\]


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