Refraction of Light
Refraction of Light
Refraction is the bending of light at the boundary of two
transparent substances
We sometimes call the transparent substances media
Refraction causes the pencil to
appear “bent”
It also causes water to appear
more shallow than it actually is
Speed of Light in Different
Media
When a light ray moves from one medium into another, it
changes speed
example: speed of a light ray in water is less than the
speed of a light ray in air
The change in speed is what causes the light ray to bend
We can predict what direction the light will bend in by looking
at the index of refraction for the two materials
Speed of Light in Different
Media
Medium
Speed of Light
(km/s)
Index of
Refraction (n)
air
300 000
1.00
ice
229 000
1.31
liquid water
226 000
1.33
vegetable oil
204 000
1.47
glass
197 000
1.52
ruby
170 000
1.76
diamond
124 000
2.42
Drawing Ray Diagrams of
Refraction
When drawing a ray diagram of refraction, you must include the following:
Incident ray: the light ray travelling through medium 1 toward the
boundary
Refracted ray: the light ray travelling away from the boundary through
medium 2
Normal: a line perpendicular to the boundary between the two media,
located where the incident ray strikes the second medium
Angle of incidence: the angle between the incident ray and the normal
Angle of refraction: the angle between the refracted ray and the normal
Drawing Ray Diagrams of
Refraction
incident
ray
normal
angle of
incidence
medium 1 (ex. air)
boundary
medium 2 (ex. water)
angle of
refraction
refracted
ray
Rules of Refraction
The rules of refraction describe what happens to light when it
travels from one medium to another
1. When travelling from a “fast” (lower n value) medium into a “slow”
(higher n value) medium, light bends toward the normal.
2. When travelling from a “slow” (higher n value) medium into a
“fast” (lower n value) medium, light bends away from the normal.
3.The incident ray, refracted ray, and normal all lie in the same
plane. The incident ray and the refracted ray are on opposite
sides of the boundary between the two media, and on opposite
sides of the normal.
Phenomena Related to
Refraction
Apparent Depth
The depth that an object in water
appears to be shallow due to the
refraction of light.
Apparent Depth
Objects in water appear to be
closer than what they actually are.
A fish will be deeper in the water than
it appears to be.
Why??
Your brain
projects the
light rays
backwards in a
straight line to
create a virtual
image in the
water.
Virtual Images and
Apparent Depth
The virtual images projected by our
brains are shallower than they
actually are….
apparent
vs. actual
depth.
Questions:
1. What does refraction mean?
2. Why does light bend when it travels between
two different mediums?
3. If light travels from a more dense to a less
dense medium, will it bend towards or away
from the normal? Include a diagram.
4. If light travels from a less dense to a more
dense medium, will it bend towards or away
from the normal? Include a diagram.
5. What do we mean by apparent depth? Why
does this occur? Draw a diagram to help
explain.