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Reflection and Refraction of Light
Dispersion: Different wavelengths have different velocities and therefore different indices of refraction. This leads to differentrefractive angles for different wavelengths. Thus the light is dispersed.The frequency does not change when n changes.
v f changes when medium changesf does not change when medium changes
Snells Law
n2=1.509
Red
n1=1.000 θ1
θ2
n1 sin1 n2 sin2
sin2 1.00sin1
1.509
sin2 1.00sin30
1.509
0.51.509
0.331
2 19.34deg
Example: If the incident angle of red light striking glass in air is 30 degrees,what is the angle of refraction?
Snell’s Law at Work
Fiber Cable
Why is light totally reflected inside a fiber optics cable? Internal reflection
n1 sin1 n2 sin2
(1.509)sin1 (1.00)sin 90 1.001 sin1 1
1.509 41.505 deg
7
n increases with frequencyBlue light bends more than red
Equilateral prismdispersing sunlight late afternoon.
What causes a Mirage
1.06
1.091.08
1.07 1.071.08
1.09
sky eye
Hot road causes gradient in the index of refraction that increasesas you increase the distance from the road
Index of refraction
t (1v1
h12 y2
1v2
h22 (w y)2 )
dtdy
0
1v1
sin I 1v2
sinR
n1 sin I n2 sinR
Proof of Snell’s Law using the Principle of Least Time
t ( 1v1
h12 y2
1v2
h22 (w y)2 )
dtdy
0
0 1v1
yh1
2 y2
1v2
(w y)h1
2 y2
0 = cv1
sin I cv2
sinR
cv1
sin I cv2
sinR
n1 sin I n2 sinR
Diagram for Last Activity in Lab07