The process of the loss of strength of a signal while propagating through a medium is

The height of an antenna is $500 \ m$. Its range is ........ $km$. (Radius of the Earth is $6400 \ km$)

For commercial telephonic communication,the frequency range adequate for speech signals is

$A$ signal of $0.1 \, kW$ is transmitted in a cable. The attenuation of the cable is $-5 \, dB$ per $km$ and the cable length is $20 \, km$. The power received at the receiver is $10^{-x} \, W$. The value of $x$ is ....... .
$[\text{Gain in } dB = 10 \log_{10}(\frac{P_0}{P_i})]$

Which characteristic of a carrier light wave is modulated for the modulation of a light wave?

If $f_a$ and $f_f$ represent the carrier wave frequencies for amplitude and frequency modulations respectively,then