Download Refraction - WordPress.com

Chapter 3
Refraction
Refraction:
 The change in direction of a light ray due to a
change in its speed
 Occurs when light ray transfers from one medium to
another medium with a different refractive index
Reflected Ray
Air
Glass
Refracted Ray
Incident Ray
r  i
R
 How much refraction occurs is dependent on the
refractive index & angle of incidence
 Light bends toward the normal when it enters a
medium of greater refractive index
Air
Water
 Light bends away from the normal when it
enters a medium of lesser refractive index
Air
Water
If angle of incidence = 0, no refraction
 Ex.

Stick bends in water

Sun looks oval when setting
“Shimmering” heat or “shimmering” roads
Why objects under water appear at different depths


Refractive Index:
 The refractive index (n) of a medium is a measure
for how much the speed of light is reduced inside
the medium
c = 3 x 108 m/s
c
n
v
v = speed of light in
a given medium
In water the speed of light is 2.25 x 108m/s. What
is the refractive index of water?
c
n
v
3 10
n
8
2.25 10
8
n  1.33
This means that light travels 1.33 times faster in air
than in water.
Medium
Refractive
Index
Air
1.0003
Water
1.33
Plexiglas
1.51
Glass (crown)
1.52
Diamond
2.42
The
higher
the
refractive
index, the
slower
light
travels
The index of refraction of diamond is 2.42. What
is the speed of light in diamond?
c
n
v
3 10
2.42 
v
8
v  1.24  10 m / s
8
Snell’s Law:
 In 1621, a mathematician noticed that when the
sin  i
incident medium is air: n 
sin  R
 Generally:
n1 sin 1  n2 sin 2
Index of refraction for
incident medium
Angle of
incidence
Index of refraction for
refracting medium
Angle of
refraction
Light travels from air into water. If the angle of
incidence is 30o, and the refractive index of water
is 1.33, what is the angle of refraction?
n1 sin 1  n2 sin 2
0
(1) sin 30  (1.33) sin  2
 2  22
0
 2  15
0
Light passes through glass (n=1.54). The angle of
incidence is 15o. Then the refracted ray leaves the
glass into the air. What is the angle of refraction
upon exiting the glass?
15
n1 sin 1  n2 sin 2
o
(1) sin 15  (1.54) sin  2
0
 2  9.68
0


n1 sin 1  n2 sin 2
(1.54) sin 9.68  (1) sin  2
0
n1 sin 1  n2 sin 2
o
A fisherman is looking
at
a
fish.
Given
that
the
index
of
(1) sin   (1.33) sin 38
refraction of water is 1.33, at what angle do the light
0
rays enter the water before reaching
the
1  35 eyes of the
fish?
i

AIR
WATER
52
38o