JEE Main & Advanced Sample Paper JEE Main Sample Paper-25

  • question_answer
    The maximum electron density in the ionosphere in the morning is \[{{10}^{10}}{{m}^{-3}}\]. At noon time, it increase to \[2\times {{10}^{10}}{{m}^{-3}}\]. Find the ratio of critical frequency at non and the critical frequency in the morning.

    A)  \[2.00\]                                    

    B)  \[2.82\]

    C)  \[4.00\]                                    

    D)  \[1.414\]

    Correct Answer: D

    Solution :

    Given, the maximum electron density in the morning \[{{N}_{\max }}\,={{10}^{10}}\,{{m}^{-3}}\] \[f_{e}^{'}\,=9\,{{({{N}_{\max }})}^{1/2}}\] \[=9{{(10)}^{1/2}}\] Critical frequency, \[f_{e}^{'}\,=9\times {{10}^{5}}\,Hz\] The maximum electron density at noon \[{{N}_{\max }}\,=2\times {{10}^{10}}\,{{m}^{-3}}\] Critical frequency, \[f_{e}^{''}\,=9({{N}_{\max }}){{\,}^{1/2}}\] \[=9\,{{(\,2\times {{10}^{10}})}^{1/2}}\] \[=9\times \sqrt{2}\,\times {{10}^{2}}\] The ratio of critical frequency at noon and critical frequency in the morning \[\frac{f_{e}^{''}}{{{f}_{e}}}\,=\frac{9\times \sqrt{2}\times {{10}^{5}}}{9\times {{10}^{5}}}\] \[\frac{f_{e}^{''}}{f_{e}^{'}}=\sqrt{2}=1.414\]


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