The document discusses refractive index, Snell's law, and total internal reflection as they relate to how light travels through different mediums. Refractive index is a measure of how much light slows down when moving between mediums. Snell's law describes how light bends when moving between mediums of different densities. Total internal reflection occurs when light hits the boundary between two mediums at an angle greater than the critical angle, causing it to be fully reflected rather than refracted.

1. Refractive Index
 This is a measure of how much light slows
down when it goes into a new 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

6. Try these:
 Careful – this time, the ray travels from water into
amber, so n1 is not 1, it is 1.33.

7. The Critical angle
 When a ray comes out of glass into air, it will bend away
from the normal. The critical angle is the angle it hits the
glass edge to refract exactly at 90 degrees.
 It is different for different mediums
n1
n2

8. Total Internal Reflection

9. Optical fibers
 The light ray is
reflected all the
way along the fiber
by total internal
reflection
 Critical Angle:
1.46
1.48