PASCO OS-8515C Basic Optics System - Manual (Page 31)

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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 1 1 : D i s p e r s i o n
31
Experiment 11: Dispersion
Purpose
The purpose of this experiment is to determine the index of refraction of acrylic at
two different wavelengths.
Theory
When light crosses the boundary between two transparent media, it is refracted.
Snell’s Law expresses the relationship between index of refraction of the first medium
(n
1
), the index of refraction of the second medium (n
2
), the angle of incidence (
θ
1
),
and the angle of refraction (
θ
2
):
(eq. 11.1)
Figure 11.1
We can assume the index of refraction of air (n
2
in this experiment) is always equal to
1.0. However, the index of refraction of acrylic (n
1
) depends on the wavelength, or
color, of the light. Therefore, the different wavelengths present in an incident ray of
white light will be refracted at different angles. The wavelength dependence of a
material’s index of refraction is known as dispersion.
Setup
1. Place the light source in ray-box mode on a
flat tabletop. Turn the wheel to select a single
ray.
2. Put the ray table in front of the light source so
the ray from the light source crosses the exact
center of the ray table (see Figure 11.2).
3. Put the acrylic D-shaped lens on the ray table
in the marked outline. Turn the ray table so
Required Equipment from Basic Optics System
Ray Table
D-shaped Lens
Light Source
n
1
θ
1
sin n
2
θ
2
sin =
Refracted ray
(n
1
> n
2
)
Incident ray
n
1
n
2
q
1
q
2
acrylic
air
90 90 80 70
60
50
60
70 80
20
30
40
10
0
10
40
30
20
70
60
50
80 90 80
50
60
70
20
30
40
10
0
10
40
30
20
50
COMPONENT
COMPONENT
NORMAL NORMAL
BASIC OPTICS
RAY TABLE OS-8465 RA
90 90 80 70
60
50
60
70 80
20
30
40
10
0
10
40
30
20
70
60
50
80 90 80
50
60
70
20
30
40
10
0
10
40
30
20
50
COMPONENT
COMPONENT
NORMAL NORMAL
BASIC OPTICS
RAY TABLE OS-8465 RA
Light Source Ray Table
Single
Ray
Figure 11.2