Question

The maximum frequency of transmitted radio waves above which the radio waves are no longer reflected back by ionosphere is ................. (N = maximum electron density of ionosphere, g = acceleration due to gravity)

• A. $gN$
• B. $g{N}^2$
• C. $g\sqrt{N}$
• D. $g^2{N}^2$

Answer 1

Answer: (C)

$g\sqrt{N}$

This is called critical frequency ,at this frequency wave will not return to earth .

$f_{cr}=\sqrt{81N}=g\sqrt{N}$