If in an amplitude modulated wave,the maximum amplitude is $14 \ V$ and the modulation index is $0.4$,then the amplitude of the carrier wave is (in $V$)

$A$ transmitting and receiving antenna have a height of $d$ meters each. The maximum distance between them for satisfactory communication in Line-of-Sight $(LOS)$ mode is $2d$ kilometers. If the radius of the Earth is $6400 \text{ km}$, then the value of $d$ is: (in $\text{ m}$)

In an amplitude modulator circuit,the carrier wave is given by $C(t) = 4 \sin(20000 \pi t)$ and the modulating signal is given by $m(t) = 2 \sin(2000 \pi t)$. The values of the modulation index and the lower sideband frequency are:

Which of the following statements is $NOT$ true regarding communication through optical fibers?

Which of the following four alternatives is not correct? We need modulation:

The sound produced by a tuning fork is a/an .....