Snells Law

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Snells Law

• Index of Refraction (n)

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POLAR BEAR REFRACTION at the SENECA PARK ZOO
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REFRACTION
Why does light bend?
fish tank
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Refraction

• The travel of light from one medium to another
• Change in wave speed
• change in wavelength
• Change in direction
• No change in frequency

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REFRACTION
N
li gt lr
incident ray
fi fr
Qi
fast
slow
Ray bends toward Normal
refracted ray
Qr
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REFRACTION
N
li lt lr
incident ray
fi fr
Qi
slow
fast
Qr
Ray bends away from Normal
refracted ray
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Fast to Slow
Slow to Fast
N
Qi
Qi
fast
slow
slow
fast
Qr
refracted ray bends toward N
refracted ray bends away from N
Qr
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Index of Refraction (n)
(speed of light in vacuum)
(speed of light in a given medium)
c 3.0 x 108 m/s
The bigger the n value, the slower the light
travels.
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Index of Refraction (n)

• MATERIAL n v
• AIR 1.0003
  c
• WATER 1.3 .77c
• GLASS 1.5 .67c
• DIAMOND 2.4 .42c

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SNELLS LAW
N
sin Q1 l1/hyp
V1ltV2
sin Q2 l2/hyp
Q1
V1
medium 1 (slow)
Q1
Q1
hyp
medium 2 (fast)
Q2
Q2
Q2
V f l
V2
f1 f2
V a l
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Snells Law
n2


n1
V a l
n1 sin Q1 n2 sin Q2
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Critical Angle (Qc)
Qi
Qi
Qc
glass
air
Qr 90
Qr
Qr
If the incident angle is equal to the critical
angle, the refracted angle 90
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Total Internal Reflection
reflected ray
QigtQc
glass
air
If the incident angle is greater than the
critical angle, the boundary behaves like a
perfect mirror.
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Total Internal Reflection
QigtQc
FIBER OPTIC CABLE LIGHT PIPE
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Total Internal Reflection
n1 sin Q1 n2 sin Q2
(slow medium)
(fast medium)
If material 2 is air, n2 1
If Q1 Qc Then Q2 90
n1 sin Qc 1 sin 90 1