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Experiment 11: dispersion, Purpose, Theory – PASCO OS-8515C Basic Optics System User Manual

Page 31: Setup, The index of refraction of the second medium ( n, The angle of incidence ( θ, And the angle of refraction ( θ, Eq. 11.1), We can assume the index of refraction of air ( n, Sin n

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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