Refraction
1
What is Refraction?

The bending or
change in direction
of light as it passes
from one substance
(medium) to
another substance
(medium) of
differing density
2
Why does light bend?

Refraction happens because the light slows
down in the new material
(the part of the beam that arrives first slows down first)
3
Rules of Refraction




Speed of light changes depending
on the medium through which it is
travelling
The angle of refraction is the
angle between the refracted ray
and the normal
Light bends toward the normal
when the speed of light in the
second medium is less than the
speed of light in the first medium
Light bends away from the
normal when the speed of light in
the second medium is greater
than the speed of light in the
first medium
4

In each diagram, draw the "missing" ray in order to
appropriately show that the direction of bending is
towards or away from the normal.
Light travels faster in
medium 2
Light travels
slower in medium 2
Light travels
fastest in medium 1
5
Basic Properties of Refraction
When a ray of light enters a medium where its speed
decreases, it is bent toward the normal.
When a ray of light enters a medium where its speed
increases, it is bent away from the normal
There is no change in direction if there is no change in
the index refraction. The greater the change in index of
refraction, the greater the change in direction.
If a ray of light goes from one medium to another along
the normal, it is not refracted, regardless of the index of
refraction
6
The Index of Refraction

The ratio of the speed of light in a vacuum (c) to
the speed of light in a medium (v) is called the
index of refraction and is represented by the
letter n.
c
n
v
This is a physical property of the
substance (like melting and boiling point)
c = speed of light in a vacuum
(3.00 x 108 m/s)
v = speed of light in the material
7
Your Turn: Sample Problem#1
What is the index of refraction of a liquid in
which the light travels at 2.04 x 108 m/s?
Answer:
8
c 3.00 x10 m / s
n 
 1.47
8
v 2.04 x10 m / s
8
The Refraction of Light
Here are some typical
indices of refraction:
9
Snell’s Law
The ratio of the sine of the angle of incidence to
the sine of the angle of refraction is
constant(for the same medium).
sin  i
n
sin  r
θi = angle of incidence
θr = angle of refraction
10
We can now write the angle of refraction in terms
of the index of refraction:
Note: the incident ray and the refracted ray are on
opposite sides of the normal
11
Snell’s Law - Practice
If light passing from water to glass has an angle of
refraction of 32°, find the angle of incidence. (nglass
= 2.42 and nwater = 1.33)
n1 = 1.33
n2 = 2.42
Θ2= 32°
θ1 = ?
n1sin(θ1) = n2sin(θ2)
sin(θ1) = n2sin(θ2)
n1
sin(θ1) = (2.42)sin32
1.33
sin(θ1) = 0.9642
θ1 = sin-1(0.9642)
θ1 = 75°
The angle of incidence is 75°
12
Snell’s Law - Practice
Calculate the angle of
refraction in the diagram
to the right.
nair = 1.00; nwater = 1.33
normal
nair sin  i  nwater sin  r
nair sin  i 1.00 x sin 60o
sin  r 

 0.651146
nwater
1.33
 r  sin 1 (0.651146)  40.60  410
13
Snell’s Law - Practice
Calculate the angle of
refraction in the diagram
to the right.
nair = 1.00; nglass = 1.52
normal
nair sin  i  nglass sin  r
nair sin  i 1.00 x sin 60o
sin  r 

 0.569753
nglass
1.52
 r  sin 1 (0.569753)  34.7 0  350
14
REFRACTION OF LIGHT PROBLEMS
1.
2.
3.
4.
5.
6.
7.
8.
The speed of light in glass is 2.0 x 108 m/s. Calculate the index of
refraction for the glass.
If light passing from water to glass has an angle of refraction of 25°,
find the angle of incidence. (nglass = 1.46 and nwater = 1.33)
The index of refraction for ethanol is 1.37. Calculate the speed of
light in ethanol.
The angle of incidence in diamond is 20°. What is the angle of
refraction in air?
The speed of light in leaded glass is 1.66 x 108 m/s. That is the
index of refraction for this type of glass?
The speed of light through a material is 1.24 x 108 m/s. What is the
material?
Light travels from air (n=1.00) into an optical fiber with an index of
refraction of 1.44. If the angle of incidence on the end of the fiber
is 22o, what is the angle of refraction inside the fiber?
What is the speed of light through alcohol?
15
Phenomenon Related to Refraction
Summarize the following phenomenon using
Internet research
Apparent Depth:
16
Phenomenon Related to Refraction
The Flattened Sun:
17
Phenomenon Related to Refraction
Mirages:
18
Phenomenon Related to Refraction
The Rainbow:
19
The Bent Spoon
•the spoon looks broken in a glass of
water
•the light rays bend as they go from
the air into the water in the glass
•the pattern of the light rays gets
distorted due to refraction.
20