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M o d e l N o . O S - 8 5 1 5 B
Experiment 5: Total Internal Reflection
Required Equipment from Basic Optics System
Light Source
Rhombus from Ray Optics Kit
Other Required Equipment
Protractor
White paper
Purpose
In this experiment, you will determine the critical angle at which total internal reflec-
tion occurs in the acrylic rhombus and confirm your result using Snell's Law.
Theory
For light crossing the boundary between two transpar-
ent materials, Snell's Law states
sin θ
n
1
where θ
is the angle of incidence, θ
1
refraction, and n
and n
1
refraction of the materials (see Figure 5.1).
In this experiment, you will study a ray as it passes out
of the rhombus, from acrylic (n = 1.5) to air (n
If the incident angle (θ
1
angle (θ
), there is no refracted ray and total internal
c
reflection occurs. If θ
= θ
1
ray (θ
) is 90°, as in Figure 5.2.
2
In this case, Snell's Law states:
n sin θ
c
Solving for the sine of critical angle gives:
sin θ
®
sin θ
= n
1
2
2
is the angle of
2
are the respective indices of
2
= 1).
air
) is greater than the critical
, the angle of the refracted
c
= 1 sin 90°
1
=
-- -
c
n
E x p e r im e n t 5 : T o t a l In t e r n a l R e f l e c t io n
Incident ray
q
1
n
1
n
2
Figure 5.1
Incident ray
q
c
n
n
= 1
air
Figure 5.2
Reflected ray
Surface
Refracted ray
q
(n
> n
)
2
1
2
Reflected ray
Refracted ray
90°
15
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