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NTA Abhyas 2020

Exam: NTA Abhyas
Year: 2020
Subject: Physics
Chapter: Communication System

NTA Abhyas 2020 · Physics · Communication System

What is the value of frequency at which electromagnetic wave must...

What is the value of frequency at which electromagnetic wave must be propagated for the D-region of atmosphere to have a refractive index of

0. 5

? Electron density for D-region is

400

electrons/cc

Options

A $200kHz$
&
B $104.2kHz$
C $208.4kHz$
D $312.6kHz$

Correct answer

C. $208.4kHz$

Step-by-step solution

Here,

N = 400

electrons c/cc

= 400 \times {10}^{6}

electrons

m^{- 3}

\mu = 0.5 = \sqrt{1 - \dfrac{81.56N}{v^{2}}}

= \sqrt{1 - \dfrac{81.56 \times 400 \times {10}^{6}}{v^{2}}}

On solving,

v = 208.4

kHz.

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