JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank EM Waves

  • question_answer
    For skywave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere [AFMC 2005]

    A)            \[\tilde{\ }1.2\times {{10}^{12}}{{m}^{-3}}\]              

    B)            \[\tilde{\ }{{10}^{6}}{{m}^{-3}}\]

    C)            \[\tilde{\ }{{10}^{14}}{{m}^{-3}}\]                                  

    D)            \[\tilde{\ }{{10}^{22}}{{m}^{-3}}\]

    Correct Answer: A

    Solution :

               If maximum electron density of the ionosphere is Nmax per m3 then the critical frequency fc­ is given by \[{{f}_{c}}=9{{({{N}_{\max }})}^{1/2}}.\] Þ \[1\times {{10}^{6}}=9{{(N)}^{1/2}}\] Þ N = 1.2 ´ 1012 m?3


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