Final answer:
When Jay starts yelling, the amplitude of his voice's sound waves increases, which leads to an increase in loudness, measured in decibels.
Step-by-step explanation:
Based on the information provided about Jay beginning to yell during an argument, an increase is most likely occurring in the loudness of the sound waves corresponding to Jay's voice. When someone yells, the amplitude of the sound waves they produce increases. This can be seen in the fact that amplitude is directly related to the volume of sound, and louder sounds have greater amplitude. The volume of these louder sounds is measured in decibels (dB), which is a logarithmic unit that describes the intensity of sound as perceived by the human ear.