REFRACTION AND SNELL’S LAW
REVIEW!
When light passes from a more
optically dense medium into a less
optically dense medium, it will bend
_______ (towards, away from) the
normal.
 When light passes from a medium
with a low index of refraction value
into a medium with a high index of
refraction value, it will bend _______
(towards, away from) the normal.
 Which angle is the angle of
incidence? Which is the angle of
refraction?

SNELL’S LAW



Snell's law (also known as Descartes' law, the
Snell–Descartes law, and the law of
refraction) is a formula used to describe the
relationship between the angles of incidence and
refraction.
𝑆𝑖𝑛 𝜃 incidence
𝑆𝑖𝑛 𝜃 refraction
Or
=
𝑛 refraction
𝑛 incidence
𝑆𝑖𝑛 𝜃 incidence * n incidence =
𝑆𝑖𝑛 𝜃 refraction * n refraction
LETS USE A SIMULATION TO SEE THE LAW!
Log on to a computer and open a web browser.
 In the browser type in this link

http://student.plattsburgh.edu/creev001/
Click Resources (on the left)
 Click PhET Simulations
 Click Bending Light (Left column, third down)
 Click Run Now
 Experiment with the simulation by changing the
angle of the laser and the index of refraction for
the materials!

EXAMPLES USING PHET SIMULATION
For the following examples use Snell’s Law to
calculate the unknown value.
 After you have calculated the value place the
protractor tool on the normal line.
 Turn on the laser. Is the value you calculated the
same as you see?

EXAMPLE 1

Given:
n incidence = 1.00
n refraction = 1.33
𝜃 incidence = 45 degrees

Find:
𝜃 refraction
SOLUTION 1

𝑆𝑖𝑛 𝜃 incidence * n incidence =
𝑆𝑖𝑛 𝜃 refraction * n refraction

𝑆𝑖𝑛 (45)*1.00 = 𝑆𝑖𝑛 𝜃 refraction *1.33

𝑆𝑖𝑛 𝜃 refraction = .532

𝜃 refraction = 32.1 degrees
EXAMPLE 2
Light travels from air into an optical fiber with
an index of refraction of 1.44.
(a) In which direction does the light bend?
(b) If the angle of incidence on the end of the fiber
is 22o, what is the angle of refraction inside the
fiber?

SOLUTION 2
(a)
In which direction does the light bend?
Toward the normal line
(b)
If the angle of incidence on the end of the fiber
is 22o, what is the angle of refraction inside the
fiber?

𝑆𝑖𝑛 𝜃 incidence * n incidence =
𝑆𝑖𝑛 𝜃 refraction * n refraction

𝑆𝑖𝑛 (22)*1.00 = 𝑆𝑖𝑛 𝜃 refraction *1.44

𝑆𝑖𝑛 𝜃 refraction = .260

𝜃 refraction = 15.08 degrees
EXAMPLE 3
Light traveling through the same optical fiber
(n=1.44) reaches the end of the fiber and exits
into air.
 If the angle of incidence on the end of the fiber is
30o, what is the angle of refraction outside the
fiber?

SOLUTION 3

If the angle of incidence on the end of the fiber is
30o, what is the angle of refraction outside the
fiber?

𝑆𝑖𝑛 𝜃 incidence * n incidence =
𝑆𝑖𝑛 𝜃 refraction * n refraction

𝑆𝑖𝑛 (30)*1.44 = 𝑆𝑖𝑛 𝜃 refraction *1.00

𝑆𝑖𝑛 𝜃 refraction = .72

𝜃 refraction = 46.05 degrees
EXAMPLE 4
A laser beam is incident at an angle of 30.0° to
the vertical onto a solution of corn syrup in
water.
 If the beam is refracted to 19.24° to the vertical,
what is the index of refraction of the syrup
solution?

SOLUTION 4

If the beam is refracted to 19.24° to the vertical,
what is the index of refraction of the syrup
solution?

𝑆𝑖𝑛 𝜃 incidence * n incidence =
𝑆𝑖𝑛 𝜃 refraction * n refraction

𝑆𝑖𝑛 30 * 1.00 = 𝑆𝑖𝑛 19.24 * n refraction

n refraction = 1.52
GRAPHING ACTIVITY








Using the PhET “Bending Light” simulation, set material 1 to
air and material 2 to water.
Place the protractor on the normal line and turn on the laser.
Open an Excel spreadsheet.
Return to the simulation. Move the laser from 0 to 80, in
increments of ten. At each stop record the angle of incidence
and angle of refraction on the excel spreadsheet.
In the spreadsheet record the sin of each angle you recorded
for both incidence and refraction. This can be done by hand or
by creating a formula.
Create a scatter graph plotting Sin (incidence) on the Y axis
and Sin (refraction) on the X axis.
Create a best fit line for the data you plotted. What can you
conclude about the slop of the line?
Make sure the graph is labeled properly. On your sheet write a
few sentences about the graph you created and how it relates
or supports Snell’s Law. Attach a copy of your graph and hand
in both sheets when finished.
EXIT SLIP

The angle of incidence and
the angle of refraction for
light going from air into a
material with a higher
index of refraction are 66.1
degrees and 42.2 degrees,
respectively.

What is the index of
refraction of this material?
 What is the material?