In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having an electron density of $10^{11} \text{ per } m^3$ (in $\text{ MHz}$)?

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

For an amplitude modulated wave,the maximum amplitude is found to be $10 \,V$ while the minimum amplitude is found to be $4 \,V$. The modulation index is

An amplitude modulated wave is represented by the expression $v_{m}=5(1+0.6 \cos 6280 t) \sin (211 \times 10^{4} t) \; V$. The minimum and maximum amplitudes of the amplitude modulated wave are,respectively:

Consider an optical communication system operating at a wavelength of $\lambda \sim 800 \, nm$. If only $1\%$ of the optical source frequency is available for optical communication,how many channels can be accommodated for a bandwidth of $8 \, kHz$?

$A$ carrier wave $v_{c}(t) = 160 \sin(2 \pi \times 10^{6} t) \text{ V}$ is made to vary between $V_{\max} = 200 \text{ V}$ and $V_{\min} = 120 \text{ V}$ by a message signal $v_{m}(t) = A_{m} \sin(2 \pi \times 10^{3} t) \text{ V}$. The peak voltage $A_{m}$ of the modulating signal is ..... .