• # question_answer Frequencies higher than 10 MHz were found not being reflected by the ionosphere on a particular day. The maximum electron density of the ionosphere on the day was near to A)  $\tilde{\ }{{10}^{10}}/{{m}^{-3}}$         B)  $\tilde{\ }{{10}^{11}}{{m}^{-3}}$ C)  $\tilde{\ }{{10}^{12}}{{m}^{-3}}$            D)  $\tilde{\ }{{10}^{13}}{{m}^{-3}}$

We know that $fC=q\sqrt{{{N}_{\max }}}$ $\Rightarrow$${{N}_{\max }}=\frac{f{{C}^{2}}}{81}=\frac{{{(10\times {{10}^{6}})}^{2}}}{81}$ $=\frac{{{10}^{14}}}{81}=1.24\times {{10}^{12}}/{{m}^{3}}$ $={{10}^{12}}{{m}^{-3}}$