American Board of Ophthalmology (ABO) Practice Exam

What optical phenomenon occurs when light changes direction from one clear medium to another?

1. Reflection

2. Diffraction

3. Refraction

4. Absorption

The correct answer is: Refraction

Refraction is the optical phenomenon that occurs when light changes direction as it passes from one clear medium to another. This bending of light happens due to a change in speed as it moves between substances with different densities. For example, light travels slower in water than it does in air, which causes it to change direction at the interface of the two mediums. The degree of bending, or refraction, is described by Snell's Law, which relates the angle of incidence and the angle of refraction to the indices of refraction of the two mediums. This principle is fundamental in many optical applications, such as in the design of lenses and the study of optical phenomena like rainbows or the apparent bending of objects submerged in water. Understanding refraction is crucial for many areas of optics and vision science, including corrective lenses for refractive errors in the eye, where manipulation of light paths is necessary to achieve focused vision.