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

Options

A. `~ 1.2 xx 10^(12) m^(-3) `
B. `~ 10^6 m^(-3) `
C. `~ 10^(14) m^(-3)`
D. `~ 10^(22) m^(-3)`

Answer

A

Explanation

The critical frequency of a sky wave for reflection from a layer of atmosphere is given by `f_c = 9(N_("max"))^(1//2)`
`implies 10 xx 10^6 = 9 (N_("max"))^(1//2)`
`implies N_("max") = ((10 xx 10^6)/(9))^(2) ~= 1.2xx 10^(12) m^(-3) `