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

The electron density of the ionospheric layer is $10^{11} \ m^{-3}$. Communication waves of frequency up to $f_c$ $MHz$ will be reflected by the ionospheric layer. Find $f_c$.

Three signals related to amplitude modulation are shown in the figure. The correct assignment of the signals is

The total maximum transmitted power in amplitude modulation if the carrier output power is $1 \ kW$ is

Which one of the following statements is $WRONG$?

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	$IV$. $65-75 \ km$