ARDMS Ultrasound Physics & Instrumentation Practice Exam 2025 - Free Ultrasound Practice Questions and Study Guide

The term that describes the area in a sound wave where the molecules are spread wider apart is rarefaction. In a sound wave, which is a type of longitudinal wave, compression and rarefaction occur in alternating regions as the wave propagates.

In the regions of compression, molecules are pushed together, leading to areas of higher pressure. Conversely, in rarefaction, the molecules are pulled apart, creating areas of lower pressure. This lower pressure region is what characterizes rarefaction, making it essential for understanding how sound waves travel through a medium. The distinction between these two regions is fundamental in wave mechanics and helps explain how sound energy is transmitted.

Other options such as absorption, which refers to the uptake of sound energy by the medium, and refraction, which involves the bending of sound waves as they pass through different mediums, do not pertain to the spacing of molecules within a medium in relation to sound wave propagation.