Reflection and Refraction of Light

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Reflection and Refraction of Light
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Parts of Unit 8
Wave Fronts and Rays Reflection Refraction Total
Internal Reflection and Fiber Optics Dispersion
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Unit 8.1 Wave Fronts and Rays
Along a wave front, all the waves have the same
phase. Rays are perpendicular to wave fronts, and
indicate the direction of propagation of the
wave. For a point source, the wave fronts are
spherical and the rays radial.
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Unit 8.1 Wave Fronts and Rays
For a plane wave, the wave fronts are planes. Far
from a point source, the waves are approximately
planar.
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Unit 8.1 Wave Fronts and Rays
We see objects because rays from them, or
appearing to be from them, enter our eyes.
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Unit 8.2 Reflection
The basic rule of reflection is that the angle of
incidence equals the angle of reflection. Note
that the angles are measured from the normal to
the surface.
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Unit 8.2 Reflection
Specular reflection is reflection from a smooth
surface.
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Unit 8.2 Reflection
Diffuse reflection is reflection from a rough
surface.
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Unit 8.2 Reflection
Reflected rays are drawn using
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Unit 8.3 Refraction
Refraction occurs because the speed of light is
different in different media. As light travels
across a boundary between media, it bends. The
relationship between the angle of incidence and
the angle of refraction is
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Unit 8.3 Refraction
Again, the angles are measured from the normal to
the surface.
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Unit 8.3 Refraction
The index of refraction is the ratio of the speed
of light in vacuum to the speed of light in the
medium.
The index of refraction is always equal to or
greater than 1.
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Unit 8.3 Refraction
The frequency of the wave stays the same, but the
wavelength of the light is shorter where the
index of refraction is greater.
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Unit 8.3 Refraction
Snells law can be rewritten using the index of
refraction
A ray bends toward the normal if the second
medium has a larger index of refraction, and away
from it if it is smaller.
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Unit 8.3 Refraction
A ray traversing a slab of glass will emerge
headed in its original direction, but displaced
sideways.
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Unit 8.3 Refraction
Mirages are formed by light refracting through
air of different temperatures (and therefore
densities).
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Unit 8.3 Refraction
Refraction can distort underwater views, make
straight objects appear bent, and make submerged
objects appear shallower than they really are.
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Unit 8.3 Refraction
Refraction through the atmosphere can make the
Sun appear flattened at sunset, and increase the
length of the day.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
When entering a medium of lower index of
refraction, the refracted ray bends away from the
normal. If the incident angle is large enough,
the angle of refraction is 90no light escapes.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
The angle for which this occurs is called the
critical angle
Light impinging on the boundary at this or a
larger angle will be reflected this is called
total internal reflection.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
Total internal reflection prisms are used in
binoculars to keep the length short.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
The index of refraction of diamond is
particularly large the multiple internal
reflections contribute to the diamonds
brilliance.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
Fiber optics use total internal reflection to
guide light along the fiber. The reflection means
that there are no losses out the sides of the
fiber.
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Unit 8.4 Total Internal Reflection and Fiber
Optics
Fiber optic array
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Unit 8.5 Dispersion
Dispersion occurs because the index of refraction
depends slightly on wavelength.
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Unit 8.5 Dispersion
Dispersion of sunlight in small drops of water
produces a rainbow.
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Summary of Unit 8
The angle of incidence is equal to the angle of
reflection. Index of refraction
Snells law for the refraction of light
Total internal reflection takes place for angles
larger than the critical angle
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Summary of Unit 8
Dispersion is the variation of the index of
refraction with wavelength. It is the source of
rainbows.