Wave Behavior2

7/29/2019 Wave Behavior2

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Wave Behavior

Another McGourty-Rideout

Production


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The Physics of Waves

All waves follow the laws of physics nomatter what type

Waves can be reflected, refracted,

diffracted, absorbed, scattered andexperience interference


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Reflection

Reflection happens when a wave bounces offan obstacle.

Specular reflection: smooth surface Angle of incidence = angle of reflection

Diffuse reflection: rough surface Reflection in all directions because angle of

incidence varies over the surface due to itsroughness


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Law of Reflection

angle of incidence= angle of reflection


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Reflection An echo -

example of areflection

Radaruses thisprinciple to

determine thesize,characteristicsof, and distance

to an object
http://localhost/var/www/apps/conversion/tmp/Radar/Radar.ppthttp://localhost/var/www/apps/conversion/tmp/Radar/Radar.ppt


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Refraction

Occurs as waves move fromone medium into another orwithin a medium, like air, thatvaries in density ortemperature

Waves bend toward the normalwhen they move from a lessoptically dense medium(faster) to a more opticallydense medium (slower)

Waves bend away from thenormal when the opposite istrue
http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1a.htmlhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1e.htmlhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1e.htmlhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1a.html


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Snells Law of Refraction

Angles are measured with respect tothe normal

2211sinsin nn
http://www.eserc.stonybrook.edu/ProjectJava/snell/http://www.eserc.stonybrook.edu/ProjectJava/snell/


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Refraction

1

2


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Index of Refraction

n = c / v

nair =1.0003 nwater = 1.33 nvacuum = 1.00

Can you explain why n is a nakednumber? Can it ever be less than 1?


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Index of Refraction Redux

n=

= electric permittivity = magnetic permeability

These describe how the material interactswith electric and magnetic fields


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Atmospheric Refraction

Causes gradual curveof light from stars and

sun

Makes sun visible 2-3

minutes beforesunrise and after

sunset


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Dispersion

The index of refraction of real materials actually depends on thefrequency of the light being bent.

Dispersion is the explanation for rainbows:

Each color has its own frequency

Each gets slowed down differently

Each comes out at a different angle


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Diffraction

Waves that havelonger wavelengths,

or lower frequencies,

diffract better thanhigh frequency waves

Diffraction patternsare determined by

both the size of theopening and the

wavelength


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Absorption

Absorption happens when the medium has theability to absorb the energy of the wave When the wave is absorbed, its energy is

transferred to the medium and the wave is

gone Gradual absorption as the wave penetratesthe medium is called attenuation

Absorption of only specific frequencies willleave gaps in the continuing wave spectrumcalled spectral absorption lines


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Absorption

Absorption at thequantum level happenswhen an individual photonhas the exact energy that

corresponds to an energygap between two energystates of the medium

The type of energy gapcorresponds directly to thefrequency of the photon


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Scattering

If the photon is absorbed and then re-emittedimmediately, it is said to be scattered How the light is scattered is dependent on the

frequency of the light and the size of theparticle it is scattering from

Some of the energy of the light is absorbed bythe scatterer and so the re-emitted light has alittle less energy


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Scattering

If the photon has a longer wavelength than thesize of the scattering particle, it is calledRayleigh scattering

In Rayleigh scattering the very long wavelengthlight is hardly scattered at all but the shorterwavelength is much more strongly scattered

Since blue light is much shorter than red, it getsmore scattered by the molecules in the air:therefore the sky is blue!


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Interference

When two or more waves come together,they superimpose or add together

The total amplitude is simply the sum(positive & negative!) of all the individual

amplitudes

The extremes of what can happen arecalled constructive interference and

destructive interference

C t ti d D t ti Al b i
http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l3c.htmlhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l3c.html


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Constructive and Destructive Algebraic

Addition

S

Constructive

(in phase)

Destructive

(180 out of phase)

S

Partially Constructive

(somewhat out of phase)

S

S

Non-coherent signals

(noise)


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Interference Fringes

Interference fringesare a series of bright

and dark bands

Sometimes straight,

sometimes circular,sometimes more

complicated
http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l3c.htmlhttp://images.google.com/imgres?imgurl=http://rst.gsfc.nasa.gov/Intro/color_hector.jpg&imgrefurl=http://rst.gsfc.nasa.gov/Intro/Part2_1c.html&h=275&w=346&sz=174&tbnid=7TW2vG6lVOEJ:&tbnh=92&tbnw=116&hl=en&start=6&prev=/images%3Fq%3Dinterference%2Bfringes%26svnum%3D10%26hl%3Den%26lr%3Dhttp://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l3c.html


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Youngs Double Slit Experiment

Light diffractingthrough 2 slitsproducesfringes on a

screen Bright fringesare areas ofconstructiveinterference

Dark fringes areareas ofdestructiveinterference
http://www.colorado.edu/physics/2000/applets/twoslitsa.htmlhttp://www.colorado.edu/physics/2000/applets/twoslitsa.html

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