Previous Knowledge


You have already learned that light travels in a
. That light is
by mirrors, regardless of whether they are plane, concave or convex. The
speed of light in a vacuum is
.
If light travels continues to travel through the same substance (ex. air only, water only), it
will travel in a
. Anytime light travels in a different medium it changes
its speed. A medium is any substance through which energy can be transferred.
The Bending of Light



Refraction is the
of light as
they pass through different medium (at the
between two transparent substances)
(ex. from air to water)
Refraction happens because the speed of light changes
when light goes through a different medium
When light travels from one medium (substance) to a
different medium (substance), light can be refracted.
Material
Speed of Light
Vacuum/Air
Water
Acrylic
Definitions and Ray Diagrams for Refraction
nair
nwater
 The
ray is the light ray travelling to the boundary.
 The
ray is the light ray travelling away from the boundary
 The normal is
to the boundary between the two media
(substances).
 The
is the angle at which the incident ray strikes the
boundary. It is the angle between the
and the
.
 The
is the angle between the refracted ray and the normal.
The Rules for Refraction
These rules predict what happens to light as it moves from one substance to another.
1. If a light ray travels from a medium in which its speed is faster to a medium in which its
speed is slower, light bends
the normal.
2. If a light ray travels from a medium in which its speed is slower to a medium in which its
speed is faster, light bends
from the normal.
3. The incident ray, refracted ray and normal are on the same plane. The incident ray and
refracted ray are on
sides of the line that separates the two media.
Sample Problem
1. Explain the difference between refraction and reflection.
2. Consider what would happen to light when it travels from air to water (Case 1) and water to
air (Case 2):
CASE 1:
LIGHT TRAVELS FROM AIR TO WATER
CASE 2:
LIGHT TRAVELS FROM WATER TO AIR
Diagram
AIR
AIR
WATER
WATER
Speed of
Light
Refracted
Ray
HOMEWORK: Read Pages 515-518 and do Questions #1-5 on Page 519