BEHAVIOR OF LIGHT
• Light acts both as a wave and as a particle
• Called a “wavicle”
• Light needs to interact with a surface in order
to be seen
• When light encounters a boundary it can
either reflect (bounce back) or refract (bend).
REFLECTION OF LIGHT
• Light reflects by bouncing back at the exact
same angle that it encounters the surface
with.
• Θi = Θr
REFRACTION OF LIGHT
• When light moves from one material to
another, its speed changes based on the
density of the new material
• Fastest light can travel is 3.0 x 108 m/s
(vacuum) = c
• The comparison of the fastest speed to the
speed in a material is called the index of
refraction, n
INDEX OF REFRACTION
The higher the index of
refraction, the slower the
speed of light in the
material.
𝑐
𝑣=
𝑛
c = 3.0 x 108 m/s
EXAMPLE…
What is the speed of light in diamond?
SNELL’S LAW
When a light ray passes from one material to
another, the light ray bends depending on the
ratio of the indices of refraction for the two
materials.
If the 1st material has a low index of refraction,
the light ray will bend toward the normal.
If the 1st material has a high index of refraction,
the light ray will bend away from the normal.
𝒏𝒊 𝒔𝒊𝒏 𝜽𝒊 = 𝒏𝒓 𝒔𝒊𝒏 𝜽𝒓
EXAMPLE…
A ray of light enters the water from the air at 60⁰ What is
the angle of the light ray in the water?
TOTAL INTERNAL REFLECTION
Sometimes a light ray is bent so much that it reflected
back within the original material.
Can only occur when traveling from a high index to a low
index of refraction.
Can only occur for one particular angle (called the critical
angle).
The refracted angle is considered to be 90 (sin 90 = 1)
EXAMPLE
What is the critical angle for diamond in air?
APPARENT DEPTH
Refraction explains why materials at depth look
higher than they really are.
𝒏𝒂𝒊𝒓
𝑫𝒂𝒑𝒑 = 𝑫𝒂𝒄𝒕 𝒙
𝒏𝒎𝒂𝒕