American Board of Ophthalmology (ABO) Practice Exam

What is the cause of optics when light expands upon entering a medium of lower density?

1. Dispersion

2. Refraction

3. Reflection

4. Absorption

The correct answer is: Refraction

The phenomenon where light changes direction and speed when it travels from one medium to another is known as refraction. This occurs due to the difference in optical density between the two media; when light moves from a medium of higher density to one of lower density, it slows down and bends away from the normal line at the interface. Refraction is pivotal in understanding how lenses work. For instance, when light enters a less dense medium, such as air from water, it expands, creating an angle of refraction that can be calculated using Snell's Law. This is crucial in the design of optical devices like glasses, cameras, and microscopes, where accurate manipulation of light paths is essential for clarity and focus. In contrast, dispersion refers to the separation of light into its different colors, reflection involves light bouncing off surfaces, and absorption pertains to the loss of light energy as it interacts with a medium. While these concepts are related to the behavior of light, they do not specifically pertain to how light behaves when transitioning between media of varying densities, which distinctly describes refraction.