PADI Divemaster Certification 2026 – 400 Free Practice Questions to Pass the Exam

The change in direction of light as it passes from one medium to another is primarily influenced by the density of the media and the speed at which light travels through those media. This phenomenon is known as refraction. When light enters a medium with a different density, its speed changes. This change in speed causes the light to bend; for example, light slows down when it enters a denser medium (like water) from a less dense medium (like air), resulting in a change in its propagation direction.

Refraction is governed by Snell's Law, which relates the angles of incidence and refraction to the indices of refraction of the two media involved. The index of refraction is affected by the optical density of the media, which is how much a material can bend light. Thus, understanding the relationship between the density of the medium and the velocity of light is crucial for predicting how light will change its path during such transitions.