Sky wave propagation is not possible for frequencies

The maximum frequency of transmitted radio waves above which the radio waves are no longer reflected back by the ionosphere is . . . . . . ($N=$ maximum electron density of the ionosphere, $g=$ acceleration due to gravity).

In amplitude modulation of waves,the maximum amplitude is $30 \text{ mV}$ and minimum amplitude is $5 \text{ mV}$,then the modulation index is

The modulation index for an $A.M.$ wave having maximum and minimum peak-to-peak voltages of $14\,mV$ and $6\,mV$ respectively is:

In an amplitude modulated signal,the maximum amplitude is $15 V$ and the minimum amplitude is $5 V$. The amplitude of the modulating wave will be (in $V$)

If the maximum and minimum voltage of an amplitude modulated wave are $V_{max}$ and $V_{min}$ respectively,then the modulation factor is: