What phenomenon does Snell's law describe?

Snell's law describes the phenomenon of refraction at an interface. Refraction occurs when a wave, such as light or sound, passes through different media with varying densities, causing the wave to change its speed and direction. Snell's law mathematically relates the angles of incidence and refraction to the velocities of the wave in both media, as well as their respective indices of refraction.

This principle is essential in ultrasound and sonography, as it explains how ultrasound waves behave when they transition between different tissues within the body, which have distinct acoustic properties. Understanding refraction is crucial for accurate imaging and interpretation in clinical practice, as it affects beam direction, focusing, and overall image quality.