Question

A layer of ionosphere does not reflect waves with frequencies greater than 10 MHz; then maximum electron density in this layer is

• A. $1.23\times {10}^{11}{m}^{-3}$
• B. $1.23\times {10}^{10}{m}^{-3}$
• C. $12.3\times {10}^{10}{m}^{-3}$
• D. $1.23\times {10}^{12}{m}^{-3}$

Answer 1

The correct option is D $1.23\times {10}^{12}{m}^{-3}$

If maximum electron density of the ionosphere is $N_{max}per{m}^{3}3$, then $f_c=9(N_{max}{)}^{1/2}$. Above $f_c$ a wave will penetrate the ionosphere and is not reflected by it.
or $N_{max}=\frac{(f_c{)}^2}{81}$
or $N_{max}=\frac{(10\times {10}^6{)}^2}{81}$
or $N_{max}=1.23\times {10}^{12}{m}^{-3}$