PASCO OS-8515C Basic Optics System - Manual (Page 15)

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M o d e l N o . O S - 8 5 1 5 C E x p e r i m e n t 4 : S n e l l ’ s L a w
15
Experiment 4: Snell’s Law
Purpose
The purpose of this experiment is to determine the index
of refraction of the acrylic trapezoid. For rays entering
the trapezoid, you will measure the angles of incidence
and refraction and use Snell’s Law to calculate the index
of refraction.
Theory
For light crossing the boundary between two transparent
materials, Snell’s Law states
n
1
sin
θ
1
= n
2
sin
θ
2
where
θ
1
is the angle of incidence,
θ
2
is the angle of
refraction, and n
1
and n
2
are the respective indices of
refraction of the materials (see Figure 4.1).
Procedure
1. Place the light source in ray-box mode on a sheet of
white paper. Turn the wheel to select a single ray.
2. Place the trapezoid on the paper and position it so
the ray passes through the parallel sides as shown in
Figure 4.2.
3. Mark the position of the parallel surfaces of the
trapezoid and trace the incident and transmitted
rays. Indicate the incoming and the outgoing rays with arrows in the appropriate
directions. Carefully mark where the rays enter and leave the trapezoid.
4. Remove the trapezoid and draw a line on the paper connecting the points where
the rays entered and left the trapezoid. This line represents the ray inside the trap-
ezoid.
5. Choose either the point where the ray enters the trapezoid or the point where the
ray leaves the trapezoid. At this point, draw the normal to the surface.
6. Measure the angle of incidence (
θ
i
) and the angle of refraction with a protractor.
Both of these angles should be measured from the normal. Record the angles in
the first row of Table 4.1.
Required Equipment from Basic Optics System
Light Source
Trapezoid from Ray Optics Kit
Other Required Equipment
Protractor
White paper
Normal to surface
Surface
Refracted ray
(n
1
> n
2
)
Incident ray
n
1
q
1
q
2
n
2
Figure 4.1
q
i
Incident ray
Figure 4.2