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Chapter 29 Reflection
and Fraction
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Reflection and Refraction
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29.1 Reflection
Waves are almost total reflected atthe wall
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Transmission into a newMedium
Waves are only partially reflected
When Light Hits waterperpendicularly about 2% is reflected
About 4% with Glass
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29.2 The Law of Reflection
Mirror
IncidentRay
RefIect
edRay
Norm
al
Angle ofIncidence Angle ofReflection
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Law of Reflection
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29.3 Mirrors
Image is Virtual because it appearsthat it is behind the mirror
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Concave and ConvexMirrors
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Again
http://sol.sci.uop.edu/~jfalward/physics17/chapter12/chapter12.html
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Telling Questions
If you look at your blue shirt in themirror, what color is the image?
What does this tell you about thefrequency of the light incidentcompared with the light reflected?
If you take a picture standing 2 maway from a mirror
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29.4 Diffuse Reflection
When Light Hits a Rough Surface
Each individual ray obeys the laws ofreflection
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Polished or Rough?
This will see like a smooth surface forlong-wavelengths
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29.5 Reflection of Sound
Echo is reflected sound
Sound not reflected is absorbed ortransmitted
Sound reflects from all surfaces The Study of the reflective property
of surfaces is called Acoustics
Multiple reflections are know as
reverberations
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Reverberations
When surfaces are too reflective thesound gets garbled.
When they aretoo absorbentthe sound isdull.
Acoustics strikea balance
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Concert Hall
Great Acoustics!
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29.6 Refraction
Wave speed changes where the airmeets the water
This is also known as a
wave front
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Refraction
Another Example
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29.7 Refraction of Sound
Uneven Winds
Sound also travels quicker in warmerair
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Telling Question
You are downwind from a factorywhistle. In which case will the whistlesound louder, if the wind is faster on
the ground or faster a few metersabove the ground?
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29.8 Refraction of Light
Wavefront is Perpendicular to thedirection of the wave
Caused by changes in c as it passesfrom one medium to another
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Index of Refraction
n = =c in a vacuum c
c in material
1
2
n sin = n sin 1 1 2 2
Snells Law
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29.9 Atmospheric Refraction
Hot air has lower n than cooler air
So light travels faster through thecooler air
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Atmospheric Refraction
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Pumpkin Sun
You see the sun even after it hasgone below the horizon.
Since the atmosphere has differentdensities
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Telling Question
If the speed if light were the same forthe different temperatures anddensities of air, would there still be
mirages? Slightly longer Daytimes?and a Pumpkin sun at sunset?
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29.10 Dispersion in a Prism
In a transparent medium, c is less.
Also different frequencies of lighttravel at different speeds
Red travels about 1% faster thanviolet
So each color bends ay a slightlydifferent angle
This is Dispersion
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29.11 The Rainbow
Classic Dispersion Example
Violet bends the most
Red the least
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Rainbow
If you were to see this from abovethe rainbow would appear like acomplete circle.
The ground gets in the way
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Rainbow Reconstructed
Higher drops trasmit the lowerfrequency light
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Telling Question
If light traveled at the same speed inraindrops as it does in air, would westill have rainbows?
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29.12 Total InternalReflection
Critical Angle for water is about 48
Glass about 43
More than that the light is internallyreflected
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Total Internal Reflection -Prisms
Will bounce around inside until theangle is less than 43
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Diamonds
Critical angle is 24.6
Smaller than another other material
What was the speed of light throughGlass?
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Optic Fibers InternalReflection Applied
Higher frequencies of Light thanElectrical Current
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13-2 The Law of Reflection
Mirror
IncidentRay
RefIect
edRay
Norma
lAngle of
Incidence
Angle of
Reflection
1
i
r
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Vocabulary
Object Distance Distance fromMirror to Object
Image distance- from Mirror to Image
Focal Point where parallel raysmeet
Focal Length - From FP to
mirror
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Vocabulary
Reflection Bouncing of Light
FL of Concave or Converging Mirror isalways +
FL of Convex or Diverging Mirror isalways -
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Mirror Equation
= +1 1 __ _1_ _focal length object distance image distance
= +o i
1 1 1_f d d
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13-2 Example 3
Reflection of a car at 40
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13-2 Example 4
= +
o i
1 1 1_
f d d
od = 15cm
id = -4cm
f = ?
= +1 1 1_
f 15cm -4cm
= -4 15_
60cm 60cm
= -11
60cm
= -60cm
11
-5.5 cm
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13-2 Example 5
= +
o i
1 1 1_
f d d
od = 6cm
id = -12cm
f = ?
= +1 1 1_
f 6cm -12cm
= -2 1_
12cm 12cm
= 1
12cm
12 cm
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13-3 Refraction
n = =c in a vacuum c
c in material
1
2
n sin = n sin 1 1 2 2
n sin = n sin 901 c 2
Critical Angle
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13-3 Example 6 Watch
n = =c in a vacuum c
c in material
c = 3 X 10 m / s8
v = 1.9 X 10 m / s8
n = ?
8
n = =3 X10 m / s1.9 C 10 m / s8
1.58
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13-3 Example 7
n = 1.33 (water)1
n = 1 (air)2
= 602
= ?1
n sin = n sin 1 1 2 2
sin =1 n sin 2 2
n1
(1) sin 60
1.33.651
= sin .6511
-1
40.6
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Chapter 29 - Objectives
Describe what happens to light whenit strikes Different materials
Describe the Law of reflection
Explain why a mirror forms a virtualImage
Describe Defuse reflection
Give Examples of ways to controlreflected sound.
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Chapter 29 Objectives
Explain the change in direction of a wavewhen it crosses a boundary between media
Describe the effects of the refraction of
sound waves Describe the effects of the refraction of light
Explain how Mirages are formed
Explain how a prism separates white light
into colors
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Chapter 29 Objectives
Describe how a rainbow is formed
Describe total internal reflection, itseffects, and its applications.
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. Section 21.3: Transverse Standing WavesSection 21.4: Standing Sound Waves and Musical Acoustics
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Web Format Powerpoint Format (.ppt)PDF Format
Web Format PDF Format
Section 21.4: Standing Sound Waves and Musical Acoustics
Side-screen Slides
Central Screen tablet notes
Applet showing pulse interference
Sinusoidal Wave Addition Applet
Animations of 1D and 2D Standing Waves
Reflection/Transmission animations:
pulse traveling from a region of low wave speed to higher wave speed. The reflected pulse is positiv
pulse traveling from a region of high wave speed to lower wave speed. The reflected pulse is negativ
http://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.htmhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.ppthttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.pdfhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.pdfhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/notes05.htmhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/notes05.pdfhttp://physics.ham.muohio.edu/waveapplets/pulseadd.htmhttp://webphysics.davidson.edu/applets/Superposition/GroupVelocity.htmlhttp://ceae.colorado.edu/~muehleis/classes/aren4020/handouts/animations/standingwaves.htmlhttp://ceae.colorado.edu/~muehleis/classes/aren4020/handouts/animations/standingwaves.htmlhttp://webphysics.davidson.edu/applets/Superposition/GroupVelocity.htmlhttp://physics.ham.muohio.edu/waveapplets/pulseadd.htmhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/notes05.pdfhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/notes05.htmhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.pdfhttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.ppthttp://www.physics.utoronto.ca/~jharlow/teaching/phy138_0708/lec05/sideshow05.htm -
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