Question

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density $10^{11}$ per $m ^{3}$ ?

• A. 2 MHz
• B. 10 MHz
• C. 12 MHz
• D. 18 MHz

Answer 1

Answer: (A)

2 MHz

Answer 2

We know that the artificial frequency of a sky wave for reflection from an ionospheric layer of the atmosphere is given by, $\upsilon_{c}=9n^{1/2}$ where $n$ is the number density of electrons/$m^3$ . It is given that $N = 10^{11} /m^3$ $\therefore \upsilon_{c}=9\times\left(10^{11}\right)^{1/2}$ $=2.8\times10^{6} Hz = 2.8 \,MHz$. Hence the wave of frequency $2 \,MHz$ will be reflected back.