Chapter 29 - Reflection and Refraction

8/8/2019 Chapter 29 - Reflection and Refraction

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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
http://www.google.com.vn/imgres?imgurl=http://farm1.static.flickr.com/144/327094224_857b413bf8.jpg%3Fv%3D0&imgrefurl=http://flickr.com/photos/jasmic/327094224&usg=__qwMYwV9_wPROUzi0DTFVc10uL_Q=&h=1440&w=1440&sz=108&hl=en&start=6&tbnid=2MLqKRekvNKYjM:&tbnh=150&tbnw=150&prev=/images%3Fq%3DImage%2BA%2BCAMERA%2BAND%2BA%2BMIRROR%26hl%3Den%26sa%3DG


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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
http://www.google.com.vn/imgres?imgurl=http://www.thelittleglasshut.com/Mirror/Cat%2520on%2520Mirror.JPG&imgrefurl=http://www.thelittleglasshut.com/Mirrors.htm&h=480&w=640&sz=28&tbnid=FhFDhqDJT5S7yM::&tbnh=103&tbnw=137&prev=/images%3Fq%3DImage%2Bof%2BCat%2Bin%2B%2Bmirror&hl=en&usg=__Rk6Dc0fNofgVZg0yaqJtNKdjGd0=&ei=7NDBSbflK4mGsQPXzan0Bg&sa=X&oi=image_result&resnum=4&ct=image&cd=1


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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


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


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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Chapter 29 - Reflection and Refraction