In which frequency range are space waves normally propagated?

For efficient transmission of sound waves of wavelength $\lambda$,the minimum length of the antenna should be.....

For an amplitude modulated wave,the modulation index is found to be $0.5$. If the maximum amplitude is found to be $10.0 \ V$,then the minimum amplitude is: (in $V$)

The process of increasing the strength of a signal using an electronic circuit is called

$A$ $TV$ transmitter has a range of $50 \ km$. The height of the $TV$ transmitter is $......$ (Radius of the earth $R_e = 6.4 \times 10^6 \ m$) (in $m$)

Match List-$I$ with List-$II$:

List-$I$	List-$II$
$A$. Troposphere	$I$. Approximate $65-75 \ km$ over Earth's surface
$B$. $E$-Part of Ionosphere	$II$. Approximate $300 \ km$ over Earth's surface
$C$. $F_2$-Part of Ionosphere	$III$. Approximate $10 \ km$ over Earth's surface
$D$. $D$-Part of Ionosphere	$IV$. Approximate $100 \ km$ over Earth's surface

Choose the correct answer from the options given below: