Question

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 10¹¹ per m³?

(a) 2 MHz

(b) 10 MHz

(c) 12 MHz

(d) 18 MHz

Answer 1

The correct option is (a) 2 MHz.

Explanation:

The critical frequency of a sky wave for reflection from an ionospheric layer of the atmosphere is given by, U_c = 9n^1/2 

where n is the number density of electrons/m3. It is given that n = 10¹¹/m³ 

U_c = 9 x (10¹¹)^1/2 = 2.8 x 10⁶ Hz = 2.8 MHz. 

Hence the wave of frequency 2 MHz will be reflected back.