What does the refractive index measure?

• A. The speed of sound in a medium
• B. The relationship between the light speeds in vacuum and a medium
• C. The angle of incidence versus the angle of reflection
• D. The density of a material in comparison to air

Answer: (B)

The refractive index is a dimensionless number that quantifies how much light slows down as it passes through a medium compared to its speed in a vacuum. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. This relationship is crucial in understanding how light bends or refracts when entering different materials, which is fundamental in optics.

A higher refractive index indicates that light travels slower in that medium than in a vacuum, leading to greater refraction. This concept is essential for applications such as designing lenses, optical fibers, and other devices that manipulate light. Understanding the refractive index helps predict how light will behave at interfaces between media with different optical densities.