Reflection
and
Refraction
1
Reflection
• Reflection is when light hits
a boundary and bounces off
• The law of reflection states
that the angle of incidence is
equal to the angle of
reflection
2
Reflection
3
Refraction
• Refraction is the
change in
direction of
waves crossing a
boundary
between two
different media
• Angle would be
measured with a
protractor!
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Refraction
Normal
θi
Medium 1
boundary
Medium 2
θr
5
Parts of a refraction diagram
• Normal – line drawn at a right
angle to the barrier between the
media
• Boundary – barrier between the
media
• Angle of incidence – angle of ray
in first media
• Angle of refraction – angle of ray in
second media
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Index of refraction
• Measure of how much light
bends when it passes into a
medium from a vacuum
• nsubstance = c / vsubstance
• Index of refraction = speed of light in a vacuum
speed of light in the medium
• c = 3.0 x 108 m/s
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If you didn’t get that…
• index of refraction = noun Optics. a
number indicating the speed of light in
a given medium as the ratio of the
speed of light in a vacuum to that in the
given medium Symbol: n Also called
index, refractive index.
• SO, NO UNITS!
Some Common values
for n…
Vacuum 1
FusedQuartz 1.4585
CrownGlass 1.52
Diamond 2.42
Air 1.0003
Salt 1.54
Whale Oil 1.460
Water 1.33
Asphalt 1.635
Lead 2.6
Ethyl Alcohol 1.36
Heavy Flint Glass 1.65
Sample problems
1. The speed of light in one type
of plastic is 2.00 X 108 m/s.
What is the index of refraction
of plastic?
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• n = c/v
• n = 3.0 x 108 m/s / 2.0 x 108 m/s
• nplastic = 1.5
2. Find the speed of light in
water (n = 1.33).
• Vwater = 2.3 x 108 m/s
Snell’s Law
• Used to determine the
angles of incidence or
refraction.
• nisini = nrsinr
• Index of refraction of 1st medium x sine of angle of incidence =
Index of refraction of 2nd medium x sine of angle of refraction
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Sample Problems
3. If a light beam in air (n =
1.0003) hits a sheet of crown
glass (n = 1.52) at 30.0, at
what angle was it refracted?
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•nisini = nrsinr
• (1.0003)sin30 = (1.52)sinθ
• θ = 19.21°
4. A ray of light in air is incident
upon a diamond at 45.0
(ndiamond = 2.42) What is the
angle of refraction?
• 16.99°
Sample Problems
5. A ray of light passing through
ethyl alcohol (n = 1.36) strikes
a solid at an angle of 75º. If
the angle of refraction is 40º,
what is the index of refraction
of the solid?
11
• nr = 2.04
Sample Problems
6. Find the speed of light in a
substance if the ray of light
enters the substance from air
at an angle of 75º to the
surface and the angle of
refraction is 80º to the surface.
• 2 steps
• Use Snell’s Law and then n = c/v
• v = 2.0 x 108 m/s