Communication on ground is through electromagnetic waves of wavelength

Statement-$1$: Sky wave signals are used for long-distance radio communication.
Statement-$2$: These signals are generally less stable than ground wave signals.

$A$ signal is to be transmitted through a wave of wavelength $\lambda$,using a linear antenna. The length $l$ of the antenna and effective power radiated $P_{eff}$ will be given respectively as: ($K$ is a constant of proportionality)

$A$ carrier wave of peak voltage $15 V$ is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of $80\%$ (in $V$)?

$A$ carrier wave of amplitude $15\,V$ is modulated by a sinusoidal baseband signal of amplitude $3\,V$. The ratio of maximum amplitude to minimum amplitude in an amplitude modulated wave is:

Sound waves cannot be transmitted directly after conversion into electrical waves because...