Announcements 10/24/12

Announcements 10/24/12 Prayer Slinkies: Please turn-in & cross out your name Lab 6 due tonight Exam 2 starts tomorrow, goes through

Tuesday evening My office hours today: only to 2:30 pm

Foxtrot

From warmup

Extra time on?a. (Nothing in particular)

Other comments?a. A Benjamin Franklin and a 12 pack of Diet

Coke says that there will be ranges and no proofs on the test.

b. I hope we do a cool demo with polarization.

c. Since we had slinkys for waves, does that mean we get plastic prisms for optics?

From Warmup In section 35.1, your book says: "The question "Is light a

wave or a particle" is inappropriate, however. Sometimes light acts like a wave, and other times it acts like a particle." Do your best to explain to a friend in junior high school what that means and how it can be possible.

a. Light is what it is, which is neither a wave or a particle. It BEHAVES sometimes like waves and particles. When we say that it behaves that way, we mean that modeling light as either a particle or a wave (depending on the situation) helps us to understand the behavior of light itself.

b. Depending on the scale with which you view light, it can be better to describe it as a particle or a wave. When studying humans, it makes more sense to describe a group of people as the collective qualities of the group, rather than as thousands of individual people. When viewing only a few people, it is better to view them as individuals.

From Warmup

http://www.empiricalzeal.com/wp-content/uploads/2011/06/wave-particle-duality.jpg

xkcd

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Wave-particle duality

Wave/particle duality Textbook: “Sometimes light acts like a wave, and other

times it acts like a particle.” Colton: Light is made up of quantum-mechanical

particles, called “photons”. Electrons, protons, etc., are also quantum mechanical particles. Quantum-mechanical particles are neither waves nor particles in the macroscopic sense, but rather we should think of the converse: “waves” and “particles” as we typically use the words are based on our observations of large-scale effects of these quantum-mechanical particles. That is, quantum mechanics says that there are no such things are "particles". All real particles exhibit both "particle" as well as "wave" behavior. Macroscopic waves and particles are manifestations of the underlying quantum effects, not the other way around.

Colloquium speaker in 2011: “Photons don’t exist. They are only quantized oscillations of electro-magnetic fields.”

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Clicker question: Which of the following scientists did not

attempt to make a measurement of the speed of light?

a. Einsteinb. Fizeauc. Galileod. Roemere. Michelson

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How did each attempt to measure it?

From warmup

A beam of light passes through a hole of diameter d in a metal plate. Under what condition are we allowed to ignore the diffraction or “spreading” of the light?

a. when lambda<<d

“Ray approximation”

lambda = d

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Next three slides: image credit to Dr. Durfee

Diffraction: spreading of light (and interfering with itself)

lambda = d/4

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lambda = d/10

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Index of Refraction

Book table

v = c/n

Index of Refraction

Song: Roy G. Biv (start at 0:30)http://www.youtube.com/watch?v=Gf33ueRXMzQ

Image: http://en.wikipedia.org/wiki/Dispersion_(optics)

red

Different wavelengths have different speeds!

Different wave-lengths (k values) have different speeds!

v = f

Dispersion! greenblue( going into material)

inside = vacuum/n

Clicker question:

Which color of light travels fastest in glass?

a. Redb. Greenc. Blued. Same

Absorption “Lorentz oscillator model”

From Peatross & Ware, textbook for Phys 471

absorption

index of refraction

increasing frequency(decreasing )

“anomalous” index of refraction

Why is blue light slower through glass than red light? It’s closer to an absorption region

Index of Refraction Light ray at boundary

1

2

fast light(smaller n)

slow light(larger n)

Snell’s Law

n1sin1 = n2sin2

1

2

fast light(smaller n)

slow light(larger n)

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From warmup

In the movies, you sometimes see an actor looking in a mirror and you can see a front view of his/her face in the mirror. During the filming of such a scene, what does the actor see in the mirror?

a. The camera!

“Time-reversal symmetry”

Law of Reflection

refl. = 1

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2

fast light(smaller n)

slow light(larger n)

refl.

Reflections occur off of any boundary, not just “mirrors”

When will you have no reflection?

Fresnel Coefficients / Fresnel Equations

2 1 1 2

1 2 1 2

v v n nrv v n n

2 1

1 2 1 2

2 2v ntv v n n

If near perpendicular (1-D problem)

2R r 2

1T r

For arbitrary angle (these eqns not needed for HW/exam)

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1 1 2 2.

1 1 2 2

cos cos

cos coss polarn n

rn n

1 2 2 1.

1 2 2 1

cos cos

cos cosp polarn n

rn n

1 1.

1 1 2 2

2 cos

cos coss polarn

tn n

1 1.

1 2 2 1

2 cos

cos cosp polarn

tn n

Look familiar??

Clicker question:

I send white light into a prism as shown below (n>1). Will the red part of the “rainbow” be on the top or the bottom of the outgoing fan of light?

a. topb. bottom

top

bottom

Demos

Reflection/refraction using water-soluble oil

“Blackboard optics”