$A$ communications Earth satellite:

Match Column $A$ (layers in the ionosphere for skywave propagation) with Column $B$ (their height range).

Column $A$	Column $B$
$A$. $D$-layer	$I$. $250-400 \ km$
$B$. $E$-layer	$II$. $170-190 \ km$
$C$. $F_1$-layer	$III$. $95-120 \ km$
$D$. $F_2$-layer	$IV$. $65-75 \ km$

$A$ $100\, V$ carrier wave is made to vary between $160\, V$ and $40\, V$ by a modulating signal. What is the modulation index?

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 $V$?

The amplitude of $15 \sin (1000 \pi t)$ is modulated by $10 \sin (4 \pi t)$ signal. The amplitude modulated signal contains frequency(ies) of
$A) 500 \text{ Hz}$
$B) 2 \text{ Hz}$
$C) 250 \text{ Hz}$
$D) 498 \text{ Hz}$
$E) 502 \text{ Hz}$
Choose the correct answer from the options given below:

$A$ $500\, Hz$ modulating voltage fed into an $FM$ generator produces a frequency deviation of $2.25\, kHz$. If the amplitude of the voltage is kept constant but the frequency is raised to $6\, kHz$,then the new frequency deviation will be.......$kHz$.