An oscillator is producing $FM$ waves of frequency $2 \text{ kHz}$ with a frequency variation of $10 \text{ kHz}$. What is the modulation index?

$A$ radar has a power of $1 \text{ kW}$ and operates at a frequency of $10 \text{ GHz}$. If it is located on top of a mountain at a height of $500 \text{ m}$,what is the maximum distance in $\text{km}$ up to which it can detect objects on the Earth's surface? (Radius of the Earth $R = 6.4 \times 10^{6} \text{ m}$)

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

This question has Statement-$1$ and Statement-$2$. Of the four choices given after the statements,choose the one that best describes the two statements.
Statement-$1$: Sky wave signals are used for long-distance radio communication. These signals are,in general,less stable than ground wave signals.
Statement-$2$: The state of the ionosphere varies from hour to hour,day to day,and season to season.

The advantages of optical fiber communication over a two-wire transmission line or coaxial cable are . . . . . . .

Match the following:

List-$I$ (Signal)	List-$II$ (Bandwidth)
$i$. Speech Signal	$a$. $4.2 \text{ MHz}$
$ii$. Music Signal	$b$. $6 \text{ MHz}$
$iii$. Video Signal	$c$. $20 \text{ kHz}$
$iv$. $T$.$V$. Signal	$d$. $2.8 \text{ kHz}$