Question

In short wave communication, waves of which of the following frequencies will be reflected back by the ionoshperic layer having electron density `10^11 " per " m^3`
A. 2 MHz
B. 10 MHz
C. 12MHz
D. 18 MHz

Answer 1

Correct Answer - A
Critical frequency `f_c=9(N_"max")^(1//2)`
where `N_"max"`=Electron density
`therefore f_c=9(10^11)^(1//2) = 9(1/10xx10^12)^(1//2)`
`=9/sqrt10xx10^6=2.8xx10^6` Hz = 2.8 MHz
`therefore ` The frequency of 2 MHz which is less than the critical frequency will be reflected.