PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM - Manual (Page 14)

Introductory Optics System 012-02744K
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➅ On a separate sheet of paper, explain your observations in terms of the straight line propaga-
tion of light. Include a diagram showing how the width of the slit images depends on the
orientation of the Light Bulb filament with respect to the Slit Plate.
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Ray Tracing: Locating the Filament
You can use the fact that light propagates in a straight line to measure the distance between
the Light Source filament and the center of the Ray Table. Figure 1.2 shows how. The rays
on the Ray Table all originate from the filament of the Light Source. Since light travels in a
straight line, you need only extend the rays backward to locate the filament. (See Step 3 in the
first part of this experiment.)
Place a piece of blank white paper on top of the Ray Table, holding it there with a piece of
tape. Make a reference mark on the paper at the position of the center of the Ray Table.
Using a pencil and straight edge, trace the edges of several of the rays onto the paper.
Remove the paper. Use the pencil and straightedge to extend each of the rays. Trace them
back to their common point of intersection. (You may need to tape on an additional sheet of
paper.) Label the filament and the center of the Ray Table on your diagram.
➀ Measure the distance between your reference mark and the point of intersection of the rays.
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➁ Use the metric scale on the Optics Bench to measure the distance between the filament and
the center of the Ray Table directly (see the note in Figure 1.2).
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➂ How well do your measurements in Steps 1 and 2 agree? Comment.
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One of the key ideas that this experiment illustrates is the ability for us to trace light rays to
their origin or apparent origin. This concept will prove most useful in future experiments.
Figure 1.2: Ray Tracing
Light Source
Filament
Component
Holder
Note: The vertical edge of the notch
on the side of the Light Source
indicates the position of the filament.
Paper
Center
Rays on Ray
Table
Slit Plate