The document discusses refractive index, which is a measure of how much light slows down when passing through a medium. It is represented by the symbol n and is calculated as the ratio of the speed of light in a vacuum to its speed in the medium. Examples of refractive index values are provided and Snell's Law is introduced, which describes how a light ray bends when moving between media of different densities.

1. Refractive Index
 This is a measure of how much light slows
down when it goes though a particular
medium.
 Symbol n
 n (vacuum) = 1
n (medium) =
c (speed of light in vacuum)
v (speed of light in medium)

2. Examples of
refractive index:

3. Try these:

4. Snell’s Law
 When a light ray travels into a denser medium, it slows down and
bends towards the nornal. When it moves into a less dense
medium, it speeds up and bends away from the normal.

5. Snell’s Law