Refractive Index.

Refractive Index.

• A. Angle of wave refraction
• B. Amount of light absorbed by water
• C. Ratio of density to depth
• D. Ratio of wave speed in vacuum to speed in medium

Answer: (D)

The main idea is how refractive index is defined. The refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in that medium, written as n = c/v. This is a dimensionless quantity: light travels fastest in a vacuum, so c is the maximum speed, and in any other medium light slows down (v < c), giving n > 1 for most materials. This definition is what governs how light bends at boundaries, via Snell’s law, where the bending depends on the refractive indices of the two media. The angle of refraction is a consequence of the refractive indices and the incidence angle, not the definition itself. The amount of light absorbed concerns attenuation, not the speed of light or its bending. The ratio of density to depth has no direct meaning for light’s propagation in a medium.

The main idea is how refractive index is defined. The refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in that medium, written as n = c/v. This is a dimensionless quantity: light travels fastest in a vacuum, so c is the maximum speed, and in any other medium light slows down (v < c), giving n > 1 for most materials. This definition is what governs how light bends at boundaries, via Snell’s law, where the bending depends on the refractive indices of the two media.

The angle of refraction is a consequence of the refractive indices and the incidence angle, not the definition itself. The amount of light absorbed concerns attenuation, not the speed of light or its bending. The ratio of density to depth has no direct meaning for light’s propagation in a medium.