Question

What is the electron density of the layer if critical frequency is 3 MHz?

(a) 11×10^12/cm^3

(b) 0.11×10^12/cm^3

(c) 1.1×10^12/cm^3

(d) 0.11×10^10/cm^3

This question was addressed to me in a job interview.

The origin of the question is Critical Frequency in section Virtual Height, Critical Frequency and Muf of Antennas

Answer 1

Right choice is (b) 0.11×10^12/cm^3

For explanation I would say: \(f_c=9\sqrt{N\, max} \)

\(N_{max}=\frac{f_c^2}{81}=\frac{(3×10^6)^2}{81}=0.11×10^{12}/cm^3\)