In a communication system,the process of superimposing a low-frequency signal on a high-frequency wave is known as:

If $E_c$ and $E_m$ are peak values of carrier and modulating signals,respectively,then for $100 \%$ modulation,

Given below are two statements
Statement $I:$ For transmitting a signal,the size of the antenna $(l)$ should be comparable to the wavelength of the signal (at least $l = \frac{\lambda}{4}$ in dimension).
Statement $II:$ In amplitude modulation,the amplitude of the carrier wave remains constant (unchanged).
In the light of the above statements,choose the most appropriate answer from the options given below.

When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant, the modulation system is

For $100\%$ modulation,what should be the value of the minimum amplitude $(E_{min})$ of the modulated wave?

The modulation index for an $A.M.$ wave having maximum and minimum peak-to-peak voltages of $14\,mV$ and $6\,mV$ respectively is: