A World of Light and Color
Activity 11
Refraction of Light
Procedure and Results Sheet
Key Questions:


How does light bend when it travels from one medium to another?
Can we quantify this bending of light?
Materials:
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Arbor Light box and power supply (1)
Single slit mask (1)
Ruler and Protractor (1 each)
White paper (several)
D-shaped plastic
D-shaped tub
Procedure:
1. On your Prediction Sheet, draw the path of the light rays as they travel through each of the
following transparent objects in air. Make sure you draw the perpendicular to the surface at
the point where the light ray strikes it.
2. Turn on the Arbor light box, place a four-slit mask on the end that has the dual filter holders,
and collimate the rays emerging from the box. Replace the four-slit mask with a single slit
mask and check your predictions on a separate piece of paper. Carefully record your
observations below.
(a)
(b)
(c)
(d)
(e)
(f)
11.1
3. Write down briefly what you observed for each of the cases from (a) to (f).
(a)
(b)
(c)
(d)
(e)
(f)
4. From your observations, answer the following questions. Support your answer using figures
(a) through (f)
(a) How does light bend when it travels from air into plastic? Does it bend CLOSER TO or
AWAY FROM the vertical line to the surface?
Kja fkj fdsj j dajf
lfjajf sf ahkjhryo h;
aoe dsfko … Kja fkj
fdsj j dajf lfjajf sf
ahkjhryo h;
aoe
dsfko Kja fkj fdsj j
dajf lfjajf sf ahkjhryo
h; aoe dsfko Kja fkj
fdsj j dajf lfjajf sf
ahkjhryo h;
aoe
dsfko
(b) How does light bend when it travels from plastic into air? Does it bend CLOSER TO or
AWAY FROM the vertical line to the surface?
11.2
STOP
HERE
5. Start with a new sheet of paper. You will use the D shaped plastic for this exercise. Draw a
straight line through the middle of the paper (along the 8.5” side). Place the edge of the D on
the line and trace out the plastic with a pencil. Draw a line perpendicular to the D passing
through its center. See the diagram below for an illustration of the setup. Arrange to have a
single light ray incident at an angle of your choosing (preferably small) on the D. Make sure
it hits the center of the D. Using the technique of connecting two dots, draw a line for the
incident ray and refracted ray. Remove the D and measure the angle of incidence and angle
of refraction with respect to the perpendicular line (normal line) using a protractor. Repeat
this process for at least two more angles and complete the table below.
Angle of
incidence
()
Angle of
refraction
()


6. About 500 years ago, Snell performed experiments similar to what you just did and found a
pattern in the data. This relationship is now called Snell’s Law and it goes something like
this:
n1 sin(1 )  n2 sin( 2 )
where,
n1 = refractive index of the medium where the incident beam is located
n2 = refractive index of the medium where the refracted beam is located
= angle of incidence
 = angle of refraction
Refractive index (n) is a material property, like density, that lets us figure out by how much
light slows down when it enters that material. Here are refractive index values for some of
common everyday material:
nair = 1.00
nwater = 1.33
nglass = 1.50
7. Use Snell's law to calculate the refractive index of the D plastic for each set of angles in your
table. Find an average of the n values from your table above.
11.3
8. Why doesn’t the light ray that comes out on the other side of the D plastic (curved part)
bend? Explain in a clear sentence.
9. At your station, you will find a large D-shaped tub. Fill it with water and carefully bring it to
your table. Swap out the D-shaped plastic with the D-shaped water filled tub. Based on
Snell’s law, do you think the light will bend more than, less than, or the same as before? Go
to your Prediction Sheet and record your answer.
10. Now use the light box to check your prediction. It might be easier to line up your incident
ray with one of your previously measured incident rays. Measure the angles of incidence and
refraction. Do the angles you measured for incidence and refraction comply numerically
with Snell’s Law? Water has an index of refraction of 1.33.
11.4