How does amplitude modulation (AM) differ from frequency modulation (FM)?

Amplitude modulation (AM) works by varying the amplitude of the carrier wave while keeping its frequency constant. This means that the strength (or height) of the wave changes in accordance with the audio or information signal being transmitted. In contrast, frequency modulation (FM) alters the frequency of the carrier wave, which corresponds to the information signal, while its amplitude remains constant. This fundamental difference leads to various characteristics in how each modulation type handles signal quality and susceptibility to interference.

AM is generally more prone to noise and static, which can distort the audio quality of the signal, since noise typically affects amplitude. In contrast, FM has a greater ability to reject noise, making it a preferred choice in many audio broadcasting applications.

The statement that AM varies the amplitude of the carrier wave, whereas FM varies the frequency, accurately captures the core difference between the two modulation techniques and highlights why FM usually provides better sound quality in challenging conditions.