Question

A light ray in passing from water to a medium (a) speeds up (b) slows down. In each case,

1. give one example of the medium.
2. state whether the refractive index of medium is equal to, less than or greater than the refractive index of water.

Answer 1

The refractive indices of the two mediums determine whether a light beam speeds up or slows down as it moves from one to the other. The refractive index quantifies how much light slows down in a particular medium in comparison to how fast it moves in a vacuum.

1. Light travels faster as it moves through a material with a refractive index greater than that of water.

   1. Example: passing from water to air.
   2. Air has a lower refractive index than water does.

2. Light travels more slowly through media whose refractive index is higher than water when it moves from water to that medium.

   1. Example: passing from water to glass.
   2. Glass has a higher refractive index than water does.

It can be concluded that light accelerates when it passes through a medium with a lower refractive index than water. When light passes through a medium with a greater refractive index than water, it slows down.