reflection and refraction
TRANSCRIPT
Reflection
When a wave reaches a boundary it is:– Partially reflected (bounces off surface)– Partially transmitted through surface.
Note• The angle of incidence is formed
between the incident ray and the normal.
• The angle of reflection is formed between the reflected ray and the normal.
http://micro.magnet.fsu.edu/primer/java/reflection/specular/specularjavafigure1.jpg
Refraction• When a wave crosses a boundary
between Medium 1 and Medium 2, the wave changes direction because it changes velocity.
• Frequency remains constant.
• Velocity changes as a result of wavelength change.
• Simulations• http://www.walter-fendt.de/ph14e/refraction.htm *******
• http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320005/simulations6e/index.htm
ExampleLess RigidMedium
More RigidMedium
Refracted ray bendstowardsthe normal.
Incident Ray
Refracted Ray
Index of Refraction, n n = c / v
• c : the speed of light in a vacuum, 3 x 108 m/sec • v : speed of light in the medium. • n : medium's index of refraction
•n>1 (Why?)
Indices of RefractionVacuum 1.00Air 1.0003Water 1.33Ethanol 1.36Crown glass 1.52Quartz 1.52Diamond 2.42
NoteWhen the incident ray travels from
a less optically dense medium (low n)
to a more optically dense medium (higher n)
then the refracted ray bends towards the normal.
Problem• What is the angle of refraction when
a ray from air with an angle of incidence of 25 o is incident to water?
• Draw the ray diagram.
• Answer: 18.5 o
Total Internal Reflection• Can occur when ray goes from higher
n to lower n.• Above a Critical angle (of incidence)
the ray is reflected, not refracted• http://www.walter-fendt.de/ph14e/refraction.htm
• For problems, set the angle of refraction to 90, and solve for critical angle
Problem• Find the critical angle for a light ray
that is incident from water to air.
• Answer: 48.8 o
Dispersion• The index of refraction of glass is different
for the colors that make up white light because the speed of light is slightly different in glass for each frequency of light. (In vacuum all colors have speed c=3x108m/s.)
ProblemThe index of refraction for crown glass for red light is 1.514.What is the speed of red light in crown glass?
Answer: 1.98 x 10 8 m/s
Mirage
http://www.warren-wilson.edu/~physics/PhysPhotOfWeek/2007PPOW/20070921RoadMirage/IMG_1444MirageCrop500.jpg