More Refraction Activities!
Making sense of the Law of Refraction; Investigating a prism
Materials
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laser pointer
prism
thick glass piece
glass slide
light station
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single slot mask and triple slot mask
beam-blocker card
viewing screen
various bottles & beam observation sheets
from previous activity
plastic cube filled with water
Refraction
When light moves from one material into another, it usually
changes direction. When going from air into anything else, it
becomes more nearly perpendicular to the surface. The angle
between the light beam and the surface increases towards 90o.
Please note that the beam does not bend "backwards":
When light moves from a material into air, it also changes direction. The angle becomes
smaller (less perpendicular), if this is possible. Note that this means that light beams
take the same path, no matter whether they are going from air into water or water into air.
When light tries to leave a material to go into air, sometimes it is completely reflected
instead. This happens when the angle between the beam and the surface is already small,
so that it can’t become a lot smaller (as would be required by the refraction rule).
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What to do: (finishing previous activity set)
11. Set up the light station with the single slot mask. Adjust it to make a narrow,
bright beam across the white screen on the table top. Place the square container in the
beam, so that light goes in one side and comes out the opposite side. Observe how the
beam is affected when you turn the container.
Draw lines on the diagrams to record what you observe. Also draw (and label) reflected
beams.
12. Suppose there is an object under water. We
will see the object when light coming from the
object reaches our eye. In the drawing at right,
the lines coming from the object represent light.
Predict what happens to the light beams when
they leave the water by continuing the lines.
13. We tell where an object is by noting the direction of the light coming from it.
Where does the underwater object of Q12 seem to be, to observers above the container?
Indicate this on the diagram.
Check: explain your prediction to an instructor
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14. Use Beam Observation Page 1 to record what happens to a light beam passing
through the upright bottle from various angles. The page has space for three
observations. For each space A, B and C:
 Move the paper into the beam so it is centered on the line
 stand the bottle in the box
 Draw on the paper the path of the light beam when it leaves the bottle.
15. Explain why the light beam changes path as you go from A
to B to C, using the result of your previous investigations.
16. Using the other two water bottles, oval and round,
explore each one in the beam, and explain how the light
beam changes path.
17. Using the three-slot mask on the light station, explore how each of
the three different water filled bottles affects the light beams.
 Using Beam Observation Page 2, stand each bottle in its place.
 For each bottle draw on the paper the three light beams – before
and after the bottle.
 Draw in how the light beam went from where it entered to where
it left the bottle. Explain why it went the way it did, using the
results of your previous investigations.
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1. Does a bottle of water make a shadow? Use what you have observed so far in this
activity to predict whether or not water bottles make shadows. Write your prediction
here:
To investigate this:
 remove the mask from the light station and leave the front open.
 Stand the screen upright
 Put the bottles between light source and screen, and look for shadows on the
screen.
Write your observations here:
2. Get out the glass triangular prism, and place it vertically in the path of the beam.
Place the prism in the light beam so that the beam hits one face (not a corner). There are
both reflected beams and refracted beams, and even beams that are both reflected and
refracted. Record your observations.
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3. Let’s try to figure out how light behaves in a prism. Here is a close-up (top view) of
your prism. The incident light beam is already drawn in. Follow the procedure below to
figure out what light does in the prism. Useful tip: Look at one surface at a time, and
don’t panic! It helps to rotate your paper so that the surface you are dealing with is
horizontally in front of you.
At almost every surface there is both a reflected and a refracted beam - in other words,
the beam splits at every surface, just as you observed with the water cube and the glass
slide. (Take this one step at a time, carefully!)
a) Draw the beam that reflects off of surface A, away from the prism.
b) Draw the (dotted) normal line and then the transmitted beam through surface A, and
extend it to and end it at surface B.
c) Draw the (dotted) normal line and then the transmitted beam through surface B, and
away from the prism.
d) A beam reflects off of surface B inside the prism - draw this beam and extend it to and
end it at surface C.
e) Draw the (dotted) normal line and then the transmitted beam through surface B, and
away from the prism.
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f) There are other reflected and refracted beams that keep going, but they’re pretty dim
and weak, so we won’t draw them.
3. If you aim the laser pointer back in along one of the outgoing beams, it will come out
in several directions. But one of these hits the light station. Explain why.
4. As you turn the prism, one of the beams becomes
colored and then abruptly disappears, while another
becomes brighter. What paths are these beams taking as
they go through the prism?
Check #3: Show your prism diagram to an instructor, and show your instructor that light
going into a prism actually behaves the way you predicted. Then discuss Q3 and Q4.
5. In diagram A, below, show what will happen to a laser beam directed towards a
wedge made of some material. In diagram B, show what happens to three parallel laser
beams.
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6. In diagram B, the light beams cross somewhere (“the focal point”) after going
through the six-sided object. Suppose instead there were a light source at the focal
point, emitting light towards the six-sided object. What would happen to these light beams?
7. If we want every parallel beam to go to the same focal point, we need an object with a
curved surface (a lens). On this diagram, continue the lines to show how the light beams
come together at the focal point.
8. Another way to accomplish this is to use many wedge-shaped pieces (this is called a
Fresnel lens (the word is pronounced “fre-NELL”). Draw lines showing how all the
light beams come together at the focal point.
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9. Lighthouses are put on reefs and islands to warn ships. If an ordinary light source
(that sends light in all directions) is used, most of the light is wasted. Draw lines
showing the light beams.
10. The solution to the light house problem is to use a Fresnel lens to direct most of the
light towards the ships. Assume the light source is placed exactly at the focal point of
the lens, and draw some lines showing how the light is redirected
11. A fish is swimming in a calm clear pond, and a bird is flying over the pond. Draw
some lines that show how the fish can see the bird, and how the bird can see the fish.
From the point of view of the fish, in what direction does the bird seem to be?
the path that light takes.
From the point of view of the bird, where does the fish seem to be?
that light takes.
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Draw in
Draw in the path
Each group should hand in one copy of this page
Group:
Names of group members present:
12. Veronica has invented a new kind of lighting fixture that has a light bulb in the
center of a square glass container filled with water. The resulting lighting is not very
uniform: some places outside the lighting fixture get lit better than others. Draw in some
light beams that shows where the light goes (please use a ruler to make straight lines).
13. A laser beam is directed towards a prism, as shown. Three visible light beams
result:
A) light that is reflected from the front surface,
B) light that enters the prism, travels to a different surface of the prism, and leaves it;
C) light that enters the prism, travels to a different surface of the prism where it is
reflected, travels to yet another surface (perhaps the first one, again), and leaves there.
Please draw in the path taken by these three beams (labeling them A, B, C)..
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