bjm5/09
Refraction of Light Lab
Name: ______________________
Partners: _______________________________________
Purpose:
Date: __________
Period: ________
To find an equation relating the angles a light ray makes with the “normal” on
either side of a border between air and water.
Dish alignment:
Place the semicircular plastic dish with water inside it on a piece of polar
graph paper, positioned according to these rules. Trace its approximate
position before doing the careful alignment described below.
1) The flat side should be parallel to the 90-270 degree line. Don’t try to put it on top of the line.
2) The scratch on the dish should be on top of the 0-180 degree line. This line is the “normal””,
the line perpendicular to the surface.
We will use a semicircular plastic dish with water inside. The flat side of the dish will be our
border between air and water. If we arrange for the light ray to pass through the midpoint of the
flat border, then it will travel along a “radius” and so will not bend at the curved border. This will
insure that all bending that happens will be at the flat border.
To collect data, make sure the laser is firing a ‘line’ of light. Fire the laser at various angles on
the flat side of the dish. The angles (measured from the ‘normal’) should range from 0 to 90
degrees. You will observe the light leaving the dish at various angles (measured from the
‘normal’).
Collect the data on the table provided. Using the polar
graph paper as a protractor, measure the angles from
the nearest normal, not from the boundary surface. To
get an idea of how much error there is in the lab, repeat
these same angles on the other side of the normal.
Define all angles as positive and list them all together in
one long data table.
You will measure the angles on the water side by
assuming they pass through the curved border without
bending and so continue on out into the air. Measuring
an angle in the air on the curved side is the same as
measuring it in the water next to the flat boundary.
normal
a
air
water
w
Q1: From your data table, select one of the angles on the curved side and fire the laser into the
dish at that angle (on the curved side). Write down the angle for the water side and the
resulting angle on the air side. What do you notice about these angles when compared to
firing from the air side?
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Q2: Which angle is consistently larger as measured from the normal, air angle / water angle ?
Q3: Imagine that the flat boundary is along the y axis of an x-y graph (note this is different from
the large diagram above). Let a light ray approach this boundary from the fourth quadrant. In
which quadrant will it pass after going through the origin? _________
Q4: In the previous diagram, if quadrants 1 and 4 are filled with water and 2 and 3 are filled with
air, will the ray in the air be closer to the x axis (the normal) than the incident ray in the
water or will it be farther from the x-axis?
closer or farther
2
3
1
4
For data analysis and conclusion, you need :
A data table of all quantities measured or graphed. Don’t split the angles collect on one side of
the normal from the other side, just put them into one long data table. Leave room on the right of
the data table for sine values. They should be labeled air or water (see diagram).
A graph of the raw data with the air side angle on the vertical axis, water angle on the horizontal
axis. (I know this is backwards, trust me!) All the angles should go together on one graph. All
values should be positive. Please use the symbols I defined in the diagram.
A graph of the sines of the angles with the air value on the vertical, water value on the
horizontal. All the sines of the angles should go on one graph. You will have only two graphs,
(angle graph and sine graph), each with only one line, straight or curved.
Finally, assume only one of your graphs is straight and write the equation for it. You may drop
the intercept. If you can’t decide which is straighter, look within your intuition for a sign (a sine?)
... Hint, Hint.
Write your equation on the graph.
If you use Graphical Analysis, use it to print labels on the graph. Also include your names.
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Name: __________________________
Air Angle
Left Side
0
10
20
30
40
45
50
55
60
65
70
75
80
Right Side
0
10
20
30
40
45
50
55
60
65
70
75
80
refraction -snell’s law Lab
SIN(a)
3
Water Angle
SIN(w)
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