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Chapter 14
Section 1: refraction
Objectives

Recognize situations in which refraction will occur.

Identify which direction light will bend when it passes from one medium to
another.

Solve problems using Snell’s law.
Refraction of light

The bending of light as it travels from one medium to another is call refraction.


As a light ray travels from one medium into another medium where its speed is
different, the light ray will change its direction unless it travels along the normal.
Frequency remains constant.

Velocity changes as a result of wavelength change.

Simulations

http://www.walter-fendt.de/ph14e/refraction.htm

http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320005/si
mulations6e/index.htm
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refraction
Refraction of light

Refraction can be explained in terms of the wave model of light.

The speed of light in a vacuum, c, is an important constant used by physicists.

Inside of other mediums, such as air, glass, or water, the speed of light is
different and is usually less than c.
refraction
Less Rigid
Medium
More Rigid
Medium
Refracted ray bends
towards
the normal.
Angle of refraction

The angle between the refracted ray and the normal
Law of refraction

An important property of substances is the index of refraction

The index of refraction for a substance is the ratio of the speed of light in a
vacuum to the speed of light in that substance.
c
n
v
speed of light in a vacuum
index of refraction 
speed of light in medium
Indices of Refraction for Various
Substances
indices
Vacuum
Air
1.00
1.0003
Water
1.33
Ethanol
1.36
Crown glass 1.52
Quartz
1.52
Diamond
2.42
Law of refraction

When light passes from a medium with a smaller index of refraction to one
with a larger index of refraction (like from air to glass), the ray bends toward
the normal.

When light passes from a medium with a larger index of refraction to one with
a smaller index of refraction (like from glass to air), the ray bends away from
the normal.

Note:The speed of light has a lower speed in a more optically dense medium
example

What is the speed of light in quartz?

Answer: 1.97 x 10
8
m/s
Law of refraction

Objects appear to be in different positions due to refraction.

Snell’s Law determines the angle of refraction
ni sin i  nr sin r
index of refraction of first medium  sine of the angle of incidence =
index of refraction of second medium  sine of the angle of refraction
Snell’s law
Snell’s Law
A light ray of wavelength 589 nm (produced by a sodium lamp) traveling
through air strikes a smooth, flat slab of crown glass at an angle of 30.0º to
the normal. Find the angle of refraction, r.
solution
Snell’s Law
Given: i = 30.0º
Unknown:
ni = 1.00 nr = 1.52
r = ?
Use the equation for Snell’s law.
ni sin i  nr sin r
 ni


–1  1.00
 r  sin   sin i    sin 
sin30.0º


 1.52

 nr

–1
 r  19.2º
video
Lets watch some videos
Student guided practice

Do problems 1-3 in your book page 487
Homework

Do worksheet