$A$ $TV$ 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 $m$)

In an amplitude modulated wave for an audio frequency of $500 \, \text{cycles/second}$, the appropriate carrier frequency will be ........ $\text{cycles/second}$.

Given below in the left column are different modes of communication using the kinds of waves given in the right column.

$A$. Optical Fiber Communication	$P$. Ultrasound
$B$. Radar	$Q$. Infrared Light
$C$. Sonar	$R$. Microwaves
$D$. Mobile Phones	$S$. Radio Waves

From the options given below, find the most appropriate match between entries in the left and the right column.

The height of a transmitting antenna at the top of a tower is $25 \; m$ and that of the receiving antenna is $49 \; m$. The maximum distance between them for satisfactory communication in $LOS$ (Line of Sight) is $K \sqrt{5} \times 10^{2} \; m$. The value of $K$ is $\dots$ [Assume radius of Earth is $64 \times 10^{5} \; m$] (Calculate up to the nearest integer value).

What is a transducer?

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