For transmission of e.m. wave of audible frequency,these waves are superimposed with waves of

Only $2 \%$ of the optical source frequency is the available channel bandwidth for an optical communication system operating at $1000 \,nm$. If an audio signal requires a bandwidth of $8 \,kHz$,how many channels can be accommodated for transmission?

$A$ signal is to be transmitted through a wave of wavelength $\lambda$,using a linear antenna. The length $l$ of the antenna and effective power radiated $P_{eff}$ will be given respectively as: ($K$ is a constant of proportionality)

An antenna current of an $AM$ broadcast transmitter modulated by $50\%$ is $11\, A$. The carrier current is.........$A$.

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

Assertion $(A)$: Television signals are received through sky-wave propagation.
Reason $(R)$: The ionosphere reflects electromagnetic waves of frequencies in the range $(3-30)$ $MHz$.
Choose the correct option.