For an amplitude-modulated wave,the maximum amplitude is $9 \ V$ and the minimum amplitude is $3 \ V$. The modulation index is ........$\%$.

The need for modulation is

$A$ diode detector is used to detect an amplitude modulated wave with $60\%$ modulation,using a capacitor of $250 \ pF$ in parallel with a resistor of $100 \ k\Omega$. What is the maximum modulation frequency that can be detected by this circuit?

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

List-$I$	List-$II$
$A$. Television signal	$I$. $03\,KHz$
$B$. Radio signal	$II$. $20\,KHz$
$C$. High Quality Music	$III$. $02\,MHz$
$D$. Human speech	$IV$. $06\,MHz$

Choose the correct answer from the options given below:

Define the following terms:
$(a)$ Ground waves
$(b)$ Trade winds

In amplitude modulation,the amplitude of the $.......$ wave varies in proportion to the instantaneous value of the $.......$ wave.