Electron number density in a layer of ionosphere is `4 xx 10^(5) cm^(-3)`. For an electromagnetic wave of frequency 40 MHz, what would be the refractive index of that layer?

Explanation

Frequency, f = 40 MHz = `40 xx 10^(6)` Hz
Electron number density,
`" " n = 4 xx 10^(5) cm^(-3) = 4 xx 10^(5) xx 10^(6) m^(-3) = 4 xx 10^(11) m^(-3)`
`therefore` Refractive index,
`mu = (1 -(81n)/(f^(2)))^(1//2) = [ 1 - (81 xx 4 xx 10^(11))/((40xx 10^(6))^(2))]^(1//2)`
` = (1 - 0.02025)^(1//2) = sqrt(0.97975) = 0.99`