The maximum amplitude of an $AM$ wave is found to be $20 \,V$ while its minimum amplitude is $4 \,V$. The modulation index is

The $T.V.$ transmission tower in Delhi has a height of $245 \ m$. The distance up to which the broadcast can be received (taking the radius of the earth to be $6.4 \times 10^6 \ m$) is .......... $km$.

The maximum amplitude of an $AM$ wave is $90 V$ and the minimum amplitude is $10 V$. What is the original amplitude of the carrier wave in the given $AM$ wave in $V$?

$A$ carrier is simultaneously modulated by two sine waves with modulation indices of $0.3$ and $0.4$; then the total modulation index is

For the propagation of $10 \ MHz$ signals as sky waves,what should be the minimum electron density in the ionosphere?

The electron density of $E, F_1, F_2$ layers of the ionosphere is $2 \times 10^{11} \, m^{-3}$,$5 \times 10^{11} \, m^{-3}$,and $8 \times 10^{11} \, m^{-3}$ respectively. What is the ratio of critical frequencies for the reflection of radio waves?