Physics 108 lecture 14: Reflection, Refraction, Polarization, Diffraction, and Interference

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Physics 108 lecture 14 Reflection, Refraction,
Polarization, Diffraction, and Interference

• Reflection
• Definition - occurs when a light wave bounces off
  the surface of an interface
• Law of Reflection - angle of incidence is equal
  to angle of reflection

incident normal reflected
?r
?i
?i ?r
Refraction Definition- bending of waves as they
pass from one substance (medium) to
another. Index of refraction light speed ratio
a measure of the amount of this bending Snell's
Law - relates index of refraction to the angle of
the light
Material 1 Material 2
?1
n1 n2
?2
Refracted into less dense
material Refracted into more dense material
?2
2
Example (Reflection) Coming from the air, an EM
X-ray wave encounters fatty tissue at an angle of
20? from the normal. At what angle does it
reflect?
Given                    Path                
Want           Conversions/Equations
Example (Refraction) Coming from the air, an EM
X-ray wave encounters fatty tissue at an angle of
20? from the normal. At what angle does it
refract?
Given                    Path              
Want         Conversions/Equations
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Polarization

• Polarization occurs when the direction of the all
  the electric fields of different light rays
  (waves) are lined up in the same direction

Diagram
Note this often happens when light bounces off
smooth surfaces ? GLARE!!
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Diffraction

• Diffraction is the bending of light waves (or
  other types of waves) around corners or through
  openings

Diagram
Note this happens at the entrances to marinas or
other restricted water areas!!
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Interference

• Interference comes from the superposition of two
  waves. That is that waves can add together (ex 
  two crests come together) or cancel out (ex a
  crest and a trough come together).

Diagram
Note you get this on your cell phone or radio or
TV (if using an antenna) sometimes