The Correct Answer and Explanation is:
The correct answer is A. amplitude modulation.
Although the specific image for “Figure 10-2” is not provided, the question describes a common scenario in physics and electronics textbooks. The answer is based on a detailed description of what each type of modulation looks like graphically.
Explanation
Modulation is the process of varying a property of a high-frequency wave, called the carrier wave, in accordance with a lower-frequency information signal, like an audio or data signal. This is done to transmit information efficiently over long distances.
A. Amplitude Modulation (AM)
In amplitude modulation, the amplitude, or the height and strength, of the high-frequency carrier wave is varied. This variation directly corresponds to the shape of the information signal. If you were to look at a graph of an AM wave, you would see a high-frequency wave whose peaks and troughs get larger and smaller. The overall shape formed by these changing peaks, known as the “envelope,” would perfectly match the original, lower-frequency information signal. The frequency of the carrier wave itself, meaning how close the individual waves are to each other, remains constant. This is the most common visual representation for a “modified carrier wave” in introductory examples.
B. Frequency Modulation (FM)
In frequency modulation, the amplitude of the carrier wave remains constant. Instead, the frequency of the carrier wave is changed in proportion to the information signal. On a graph, an FM wave would have a constant height. However, the waves would be squeezed closer together (higher frequency) to represent a positive part of the information signal and spread further apart (lower frequency) to represent a negative part.
C. Velocity Modulation
Velocity modulation is a different and more complex process primarily used in high-frequency devices like klystrons. It involves changing the velocity of an electron beam, which causes electrons to bunch together. This process is not typically represented by a simple waveform graph in the same context as AM and FM. Therefore, it is highly unlikely to be the correct answer for a standard figure showing a modified wave.
Based on these descriptions, Figure 10-2 almost certainly shows a wave with a constant frequency but varying amplitude, which is the definition of amplitude modulation.
