16 Mar 26 Soap Bubble, Photoelectric, Wave Particle Duality Actual

Today: Soap Bubble, Photoelectric Effect, Electron Waves New Reading, Exercises, HW Activity, and Quiz posted this weekend

Interferometers are great physics tools ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Also in space! LISA (2018)

Much of the physics of polarized light, diffraction and interference are illustrated by a CD & DVD Player! ,[object Object],Diffraction Grating Tracks in a CD Spacing about ½ micron Pits in a CD

Much of the physics of polarized light, diffraction and interference are illustrated by a CD & CD Player! ,[object Object],http://hyperphysics.phy-astr.gsu.edu/HBASE/audio/cdplay.html Destructive interference for detection

Information density is limited by laser spot size (and thus wavelength of laser) Blue lasers more difficult to make than red lasers

Interference from thin films ,[object Object],Fast Slow Fast

A soap bubble or film is a thin layer of water stabilized by detergent molecules http://www.funsci.com/fun3_en/exper2/exper2.htm Water: speed of light slower Air: speed of light fast Air Incident light will reflect and pass through interfaces. Reflections off the top surface and bottom surface will interfere with each other KEY POINT: 180 degree phase shift when reflecting off interface going from fast to slow (top interface in this case) Detergent layer

180 degree phase shift explains the black color in the thinnest part of the soap film http://www.funsci.com/fun3_en/exper2/exper2.htm Water: speed of light slower Air: speed of light fast Air When film is very thin, path length difference is negligible. So interference is destructive . Appears black because I used black mug. As film gets thicker, there is some path length difference, so interference is not completely destructive – white color. Wikipedia.org Detergent layer

Clicker Question—Thin film interference ,[object Object],[object Object],GLASS (Slower than water)

Clicker Question—Thin film interference ,[object Object],[object Object],[object Object],GLASS (Slower than water)

[object Object],Fast Slow Fast

Let’s Brainstorm: Everyday examples of interference? Where in nature do you see sunlight (or indoor lights) being spread into colors? ,[object Object],[object Object]

So, we have seen a bunch of demonstrations of wave properties of light… ,[object Object]

Einstein’s 1905, It was a very good year! ,[object Object],[object Object],[object Object]

What evidence do we have that light acts like a wave? Brainstorm! (Thanks to Katie Richardson-McDaniel for next many slides)

[object Object],[object Object],[object Object],[object Object],What evidence do we have that light acts like a wave? ,[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],What if light were made of individual packets of energy, called quanta? ,[object Object]

[object Object],[object Object],How can we tell if Planck was right? ,[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Clicker Question: How do you think light will behave when we shine it on a metal?

Let’s try our own demo of the photoelectric effect First, let’s try the experiment with an applet to get familiar with apparatus http://www.ifae.es/xec/phot2.html Explanatory video: http://www.youtube.com/watch?v=N7BywkIretM

Post-Experiment Discussion Point: Does this finding change the wave-like observations we've made before?

The photoelectric effects proves that light comes in discrete packets (photons) ,[object Object],[object Object],[object Object]

Clicker question—photoelectric effect ,[object Object],[object Object],[object Object],[object Object],Red photon energy Blue photon energy Photon energy = h * frequency Metal Air Energy

Take-home message from all of this: ,[object Object],Photoelectric effect Diffraction Interference Fluorescence

Clicker Question--Electrons ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Clicker Question--Electrons ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],It turns out that matter (electrons) behaves like waves and particles too!

Well, if electrons can behave like waves… ,[object Object],[object Object],http://www.columbia.edu/~ac558/jj1.jpg

Electron microscopy particularly useful for surface science Single-atom thick silicon islands Gayle Thayer—Sandia / IBM IBM—Pentacene islands on Silicon (Imaging photoelectric effect!, PEEM) Boron growth on silicon--Sandia

Next up is nuclear physics!! Homework problem Thin film interference in your kitchen Make your own videos / pictures! ,[object Object]

16 Mar 26 Soap Bubble, Photoelectric, Wave Particle Duality Actual

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16 Mar 26 Soap Bubble, Photoelectric, Wave Particle Duality Actual