If the maximum and minimum amplitudes of a modulated wave are $25 \ V$ and $5 \ V$ respectively,then the modulation index is

In the process of space communication,the use of a modem is necessary. In which one of the following modes does a modem act as a modulator and a demodulator respectively?

In the process of modulation,the audio waves are called ...........

$A$ layer of the atmosphere that reflects medium-frequency radio waves and is ineffective during the night is

An amplitude modulated wave is represented by $10[1+0.6 \sin(40 \times 10^3 t)] \sin(4 \times 10^6 t)$ volt,where $t$ is in seconds. The ratio of the upper sideband frequency to the lower sideband frequency is:

The maximum peak-to-peak voltage of an $AM$ wave is $24 \, mV$ and the minimum peak-to-peak voltage is $8 \, mV$. The modulation factor is.....$\%$