PADI Divemaster Certification Practice Exam

What happens to light when it passes through substances of different densities?

1. It stops completely

2. It remains unchanged

3. It changes speed and direction

4. It becomes invisible

The correct answer is: It changes speed and direction

When light passes through substances of different densities, it changes both speed and direction. This phenomenon is known as refraction. Refraction occurs because light travels at different speeds in different media; for instance, it moves slower in water than in air. When light enters a new medium at an angle, the change in speed causes the light to bend towards or away from the normal, which is an imaginary line perpendicular to the surface at the point of entry. Understanding refraction is crucial in various applications, including optics and underwater navigation. It also explains why objects appear distorted or at different positions when viewed through water. This concept is fundamental to many aspects of diving, such as understanding how visual perception changes underwater compared to above water.