Question

For sky wave propagation of 10 MHz signal, what should be the minimum electron density in ionosphere?

• A. ∼ 1.2 x 10¹² m^-3
• B. ∼ 10⁶ m^-3
• C. ∼ 10¹⁴ m^-3
• D. ∼ 10²² m^-3

Hint:

The critical frequency for sky wave propagation fC = 9(N)1/2.

Answer 1

The Correct Option is A

The critical frequency of sky waves undergoing reflection from an atmospheric layer is \({{f}_{c}}=\sqrt[9]{{{N}_{\max }}}\) 
where N is electron density per m³
\(\therefore\) N_max =  \(\frac{{{f}_{c}}^{2}}{81}=\frac{{{(10\times {{10}^{6}})}^{2}}}{81}\)

= ∼ 1.2 x 10¹² m^-3

Answer 2

The critical frequency for sky wave propagation f_C = 9(N)^1/2

where N denotes the number density of electron m^-3.

10 x 10⁶ = 9(N)^1/2

\(N=(\frac{10×10^6}{9}​)^2\)

= ∼ 1.2 x 10¹² m^-3

Answer 3

Critical frequency, \(f_c​=9\sqrt{N}​=\frac{f_c^2}{81}​​\)

= ∼ 1.2 x 10¹² m^-3

Therefore, For sky wave propagation of 10 MHz signal, the minimum electron density in ionosphere is ∼ 1.2 x 10¹² m^-3.