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AIIMS 2005
Exam
AIIMS
Year
2005
Subject
Physics
Chapter
Communication System

AIIMS 2005 · Physics · Communication System

For skywave propagation of a 10 MHz signal, what should be the...

For skywave propagation of a 10MHz10 \mathrm{MHz} signal, what should be the minimum electron density in ionosphere?

Options

  1. A∼1.2×1012 m−3\sim 1.2 \times 10^{12} \mathrm{~m}^{-3}
  2. B∼106 m−3\sim 10^6 \mathrm{~m}^{-3}
  3. C∼1014 m−3\sim 10^{14} \mathrm{~m}^{-3}
  4. D∼1022 m−3\sim 10^{22} \mathrm{~m}^{-3}.

Correct answer

A. ∼1.2×1012 m−3\sim 1.2 \times 10^{12} \mathrm{~m}^{-3}

Step-by-step solution

The critical frequency of a sky wave for reflection from a layer of atmosphere is given by f_c=9\left(N_{\max }\right)^{1 / 2} where NisthedensityofelectronN is the density of electron/ \mathrm{m}^3..10×106=9(Nmax⁡)1/2Nmax⁡=(10×1069)2≃1.2×1012 m−3\begin{aligned}10 \times10^6 & =9\left(N_{\max }\right)^{1 / 2} \\ N_{\max } & =\left(\frac{10 \times 10^6}{9}\right)^2 \simeq 1.2 \times10^{12} \mathrm{~m}^{-3} \end{aligned}$
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