SNC 2D: Refraction
As we have already learned, light travels in a straight line,
however when light passes from one medium to another it will
bend or refract. This bending of light is known as refraction.
Refraction is the cause of many interesting optical effects such
as the spoon appearing to broken in the glass as a result of light
rays changing direction as they move from the air into the water.
(see fig. 1)
Fig. 1.
Fig. 2
Refraction results from light changing speed as it passes from
one medium to another. For example, as light moves from air
into the water, its speed decreases. The more profound the
change in speed the greater the refraction. Different mediums
affects on the speed of light will vary depending on the makeup
or composition of the substance. Light travels at a whopping
speed of 3.00 x 108 m/s in the vacuum of space. At this speed
light could travel seven times around the Earth in one second –
now that’s what I’m talking about.
You might be wondering – how on Earth do medium slow down the
speed of light. To understand this concept we must first recall
that a ray of light is a form of electromagnetic radiation that is
transmitted in waves. Therefore the particles in a medium can
slowdown the transmission of these waves, which results in light
travelling more slowly through a block of glass than in the vacuum
of space where it travels uninhibited. The effects of changes in the
speed of light can be seen in fig. 2.
Note: as the light enters the Plexiglass it slows down and
refracts and when the light leaves the Plexiglass it speeds up and
refracts again.
Please note that the light only refracts as it enters or
leaves the medium and not inside the medium.
Index of Refraction
The rate at which a transparent medium decreases the speed of
light can be indicated by a number value known as the index of
refraction also called the refractive index. Because light travels the
fastest in a vacuum, it is assigned a refractive index of 1.00. This
value is also assigned to air. All mediums that decrease the speed
of light more than air will have a index of refraction value greater
than 1.00.
Formula
Index of refraction of material
Index of Refraction for
Selected Media
Media
Index of
Refraction
Vacuum
1.00
Air
1.0003
Carbon
1.0005
dioxide
Water
1.33
Alcohol
1.36
Pyrex
1.47
glass
Plexiglass
1.49
Table salt
1.51
Flint glass
1.61
Sapphire
1.77
Cubic
2.16
zirconia
Diamond
2.42
Gallium
3.50
phosphide
SNC 2D: Practice Problems
1. The speed of light in a sample of glass is 1.91 x 108 m/s. The
speed of light in a vacuum is 3.00 x 108 m/s. What is the
refractive index of this glass?
2. The speed of light in leaded glass is 1.66 x 108 m/s. What is the
index of refraction of this type of glass?
3. What is the speed of light in water given that water has a
refractive index of 1.33?
4. The speed of light in quartz is 2.1 x 108 m/s. What is the index
of refraction of quartz?
5. The speed of light through a material is 1.24 x 108 m/s. What
material is it?
6. What is the speed of light through alcohol?
7. What is the speed of light through gallium phosphide?
8. What is the speed of light through sapphire?
9. The speed of light in a vacuum is 3.00 x 108 m/s. The speed of
light in medium is 1.24 x 108 m/s. Determine the index of
refraction. What might the medium be?
10.
The index of refraction of crown glass for violet light is 1.53
and for red light 1.54. What are the speeds of violet light and
red light in crown glass?
11. What is the n of refraction of a liquid in which light travels at
2.50 x 108 m/s?
12.
The index of refraction of diamond is 2.42. What is the
speed of light in diamond?
13.
What is the speed of light in sodium chloride expressed in
terms of light in a vacuum?
14.
Calculate the speed of light in zircon and express the speed in
terms of C, the speed of light.
15.
What is the refractive index for a medium where the speed is
1.65 x 108 m/s.
16.
Light travels from medium A to medium B. The angle of
refraction is greater than the angle of incidence.
a) What medium has the higher index of refraction?
b) In which medium does the light travel faster?
17.The speed of light is an unknown medium is 1.95 x 108 m/s.
Determine the index of refraction and the type of medium.
18.
Given the speed of light in air is 3.00 x 108 m/s find the
speed of light in gallium phosphide.
Answers: 1.57, 1.81, 2.26 x 108 m/s, 1.43, 2.42 (diamond), 2.21 x 108
m/s, 8.57 x 107 m/s, 1.69 x 108 m/s, 2.42 (diamond), v=1.96 x 108
m/s, r=1.95 x 108 m/s, 1.20, 1.24 x 108 m/s, 1.99 x 108 m/s, 1.39 x
108 m/s, 1.82, a=A, b=B, 1.54, 1.05 x 109 m/s