Download index of refraction

Lesson 5
Objective:
 You will be able to qualitatively and
quantitatively describe the behavior of
waves as they pass from one medium to
another.
Definition:
 Refraction occurs when a wave changes
the direction in which it is moving.
 This is caused by a change in speed as
the wave passes from one medium to
another.
 Official definition: the bending of a ray
of light as it passes obliquely between
two mediums of different density
Broken Pencil
 As light travels from
the water into the
air, its path changes
because light travels
at different speeds,
and the pencil
appears to be
broken.
How It works
Why It Works
 The light ray bends as it moves from one medium
(water) to another (air).
 We “see” the pencil at the end of a straight line.
 The light ray bending is refraction.
Waves
 If waves slow
as they go
from one
medium to
another, they
bend toward
the normal.
*
*
Index of Refraction
 n is the index of refraction and is a ratio of how much
light bends when it enters a different medium.
 The n for a vacuum is exactly 1.0000...
 Every substance has a unique optical density. The
index of refraction is used to describe the optical
density of different materials.
 The n for air is 1.0003.
Index of Refraction
medium
air
water
crown glass
quartz
flint glass
diamond
n(index of refraction)  The greater the
index the more light
1.00
bends or slows
1.33
down. This means
that all indices will
1.50 - 1.52
be greater than 1.00.
1.54
 Table on pg. 667
1.62 - 1.95
gives more
2.42
refractive indices for
various mediums.
Memory Trick
 MLA: more to less, away
 Light moving from a more dense medium (slower
speed) into a less dense medium (faster speed) will
bend away from the normal.
The Law of Refraction
Snell's Law
sin  1 v1 1 n2
 

sin  2 v2 2 n1
Example
Laser light ( = 6.33 x 10 –7 m) travels from air (n = 1.00) to glass (n = 1.50) at
an angle of 47.3  to the normal.
a) Calculate the velocity of laser light in the
glass.
47.3 
air
glass
b) Calculate the angle of refraction.
c) Calculate the wavelength of the laser in the glass.
*
a) Calculate the velocity of laser light in the glass.
n2 v1
v n

 v2  1 1
n1 v2
n2

8 m
3
.
00

10

1.00
m
s
 2.00 x 10 8
v2  
s
1.50
b) Calculate the angle of refraction.

sin 1 n2
sin 1  n1

 sin 2 
sin 2 n1
n2

sin 47.3   1.00
sin  2 
1.50
 2  29.3 
c) Calculate the wavelength of the laser in the glass.
1 n2
 n

 2  1 1
2 n1
n2
2

6.33  10


7
m 1.00
1.50
2  4.22  10
7
m
*
Example #2
 Light goes from air into water (n=1.33) with an angle of
incidence of 54.1°. Determine the angle of refraction.
Calculation:
Example #3
 Light goes from water (n = 1.33) into diamond (n =
2.42). The light ray in the diamond makes an angle of
72.8° w.r.t. the boundary between the two media.
Determine the angle of the light ray w.r.t the normal in
the water.
Water to diamond: opposite of MLA,
ray will bend toward the normal.
Calculation:
Homework:
 Workbook
 P.229 #9,10
 P.205 #3,4,8,9,10,12