Final answer:
A voltage-controller amplifier (VCA) is used to vary the sound's amplitude, which affects its volume. The energy of the sound wave, and thus its volume, is proportional to the amplitude squared.
Step-by-step explanation:
A voltage-controller amplifier (VCA) is used to vary the amplitude of the sound. Amplitude, or the size of a wave from peak to trough, directly affects the volume of the sound we hear. Sound waves with greater amplitude will result in louder sounds, and this is represented by higher decibels (dB). The pressure amplitude of a sound wave, denoted as Ap, is related to its energy and volume.
The energy, depicted as kinetic energy (m2), of an oscillating element of air due to a traveling sound wave is proportional to the amplitude squared, thereby affecting the volume. Therefore, a VCA can control the loudness of the sound by adjusting its amplitude, based on the user's input voltage.