The Correct Answer and Explanation is:
Based on the provided image where option A is selected, the correct answer is:
A. amplitude modulation
Explanation
Although the image provided does not show the actual “Figure 10-2,” the selected answer indicates that the figure illustrates a wave that has undergone amplitude modulation. This explanation will describe what such a figure would show.
Modulation is the process of encoding information onto a carrier wave. A carrier wave is a high frequency wave that is well suited for transmission over long distances. The information to be sent, such as an audio or video signal, is called the modulating signal.
In amplitude modulation, or AM, the amplitude of the carrier wave is varied in proportion to the modulating signal. The amplitude refers to the wave’s height or intensity. Imagine the carrier wave as a steady, high frequency signal. When an information signal is applied, the peaks and troughs of the carrier wave are made larger or smaller to match the shape of that information signal. A key visual characteristic of an AM wave is that its overall shape, or “envelope,” mirrors the original information signal. However, the frequency of the carrier wave, which is the spacing between the individual wave cycles, remains constant.
This process is different from frequency modulation, or FM. In FM, the amplitude of the carrier wave remains constant, but its frequency is varied by the information signal. A loud part of an audio signal would cause the waves to become more compressed (higher frequency), while a quiet part would cause them to spread out (lower frequency).
The term “velocity modulation” is less common in this context and typically relates to changing the speed of electrons in a beam, which is not a standard method for modifying radio waves. Therefore, if Figure 10-2 showed a wave with constant frequency but a varying height that traces the shape of another signal, it would be a clear depiction of amplitude modulation.
