The maximum distance up to which $TV$ transmission from a $TV$ tower of height $h$ can be received is proportional to

What should be the height of a transmission antenna (in $m$) to cover a range of $128 \, km$?

The intensity of a light pulse travelling along a communication channel decreases exponentially with distance $x$ according to the relation $I = I_0 e^{-\alpha x}$,where $I_0$ is the intensity at $x = 0$ and $\alpha$ is the attenuation constant. The attenuation in $dB/km$ for an optical fibre in which the intensity falls by $50$ percent over a distance of $50 \ km$ is

An amplitude modulated wave is represented by $c_m(t)= 10[1+0.6 \sin (1250 t)] \sin (10^8 t)$. Then the modulation index is

For amplitude modulated wave broadcast, which of the following conditions is suitable?

Find the modulation index of an $AM$ wave having $8\,V$ variation where maximum amplitude of the $AM$ wave is $9\,V$.