Download total internal reflection

Chapter 26
Geometrical Optics (Lecture III)
Dr. Jie Zou
PHY 1161
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Outline
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Features of refraction
Optical illusions caused by refraction
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Total internal reflection
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Apparent depth
Real world application: Optical fibers
Dispersion and the rainbow
Dr. Jie Zou
PHY 1161
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Features of Refraction
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When a ray of light enters a medium where its speed
decreases, it is bent toward the normal.
When a ray of light enters a medium where its speed
increases, it is bent away from the normal.
There is no change in direction of propagation if
there is no change in index of refraction. The greater
the change in index of refraction, the greater the
change in propagation direction.
If a ray of light goes from one medium to another
along the normal, it is undeflected, regardless of the
index of refraction.
Dr. Jie Zou
PHY 1161
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Conceptual Checkpoint 26-4
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A horizontal ray of light
encounters a prism, as
shown in the first diagram.
After passing through the
prism, is the ray (a)
deflected upward, (b) still
horizontal, or (c) deflected
downward?
Dr. Jie Zou
PHY 1161
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Optical Illusions Caused by
Refraction
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Apparent depth: an
object appears to be
closer to the water’s
surface than it really is.
Dr. Jie Zou
PHY 1161
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Total Internal Reflection
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For angles of incidence greater than the critical angle, it
is observed that all the light is reflected back into
the water. This phenomenon is referred to as total
internal reflection.
The critical angle for total internal reflection can be found
by sin c = n2/n1.
Total internal reflection can only occur on the side of an
interface that has the greater index of refraction.
Dr. Jie Zou
PHY 1161
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Real World Applications
Example: An optical fiber
Dr. Jie Zou
PHY 1161
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Dispersion and the rainbow
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Dispersion: The “spreading out” of light
according to color is known as dispersion.
Explanation:
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Dr. Jie Zou
The index of refraction for a given material
depends on the frequency or wavelength of the
light.
In general, the higher the frequency, the
higher the index of refraction.
Violet light bends more than red light does
when refracted by a given material.
Light of different frequencies is bent at
different angles when incident on a refracting
material.
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Formation of a rainbow
Refraction of sunlight by a
spherical raindrop.
Dr. Jie Zou
The formation of a rainbow.
PHY 1161
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