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

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soap bubble intereference, photoelectric effect, wave-particle duality of light

soap bubble intereference, photoelectric effect, wave-particle duality of light

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  • 1. Today: Soap Bubble, Photoelectric Effect, Electron Waves New Reading, Exercises, HW Activity, and Quiz posted this weekend
  • 2. Interferometers are great physics tools
    • Proved there is no “luminiferous ether”
    • Michelson-Morley Experiment 1887
    • http://www.youtube.com/watch?v=7ORSeqytMR8&NR=1
    • Laser Gyroscopes
    • Currently trying to detect gravitational waves
    • LIGO
    • LIGO video from 1:17 to 2:52
    • http://www.youtube.com/watch?v=UxpMTj2pHO4
    Also in space! LISA (2018)
  • 3. Much of the physics of polarized light, diffraction and interference are illustrated by a CD & DVD Player!
    • Look at light diffracted off a CD It’s a diffraction grating!
    Diffraction Grating Tracks in a CD Spacing about ½ micron Pits in a CD
  • 4. Much of the physics of polarized light, diffraction and interference are illustrated by a CD & CD Player!
    • A CD Player uses polarized laser light for reading the CD
    http://hyperphysics.phy-astr.gsu.edu/HBASE/audio/cdplay.html Destructive interference for detection
  • 5. Information density is limited by laser spot size (and thus wavelength of laser) Blue lasers more difficult to make than red lasers
  • 6. Interference from thin films
    • When a wave reflects from a boundary between fast and slow, there is a 180 degree phase shift
    Fast Slow Fast
  • 7. 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
  • 8. 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
  • 9. Clicker Question—Thin film interference
    • What if we had a thin layer of water on glass? In a very thin film (say 20 nanometers), would there be destructive or constructive interference?
    • A) Destructive B) Constructive
    GLASS (Slower than water)
  • 10. Clicker Question—Thin film interference
    • What if we had a thin layer of water on glass? In a very thin film (say 20 nanometers), would there be destructive or constructive interference?
    • A) Destructive B) Constructive
    • Both the top and bottom reflection would undergo a 180 degree phase shift
    GLASS (Slower than water)
  • 11.
    • Let’s look at a soap film demo
    Fast Slow Fast
  • 12. Let’s Brainstorm: Everyday examples of interference? Where in nature do you see sunlight (or indoor lights) being spread into colors?
    • Sprinklers, rainbows, waterfalls, diffraction grating
    • Bubbles, oil caked onto a cooking pan (thin film of oil) (gasoline on pavement), prisms ,
  • 13.  
  • 14. So, we have seen a bunch of demonstrations of wave properties of light…
    • Now we will see that light behaves like a particle too!
  • 15. Einstein’s 1905, It was a very good year!
    • March, 1905 – Photoelectric effect explained by “light quanta” (photons)
    • May 1905 – Mathematical explanation of Brownian motion
    • June 1905 – Relativity principle (special relativity)…new understanding of space and time.
  • 16. What evidence do we have that light acts like a wave? Brainstorm! (Thanks to Katie Richardson-McDaniel for next many slides)
  • 17.
      • Interference patterns (soap bubbles, etc)‏
      • Reflection and refraction
      • Huygens' principle
      • Diffraction
    What evidence do we have that light acts like a wave?
      • Key point: The energy of a wave can be increased by increasing the amplitude of the wave.
      • Any frequency wave can have any amount of energy!
  • 18.
      • Max Planck suggested this in 1901.
        • Einstein worked out mathematics in 1905
      • Each packet would carry an energy, E = h f
      • h is Planck's constant
    What if light were made of individual packets of energy, called quanta?
      • Key point: The energy of a single packet (photon) can only be increased if the frequency is increased.
  • 19.
      • It is possible to produce free electrons by shining light on a sheet of metal.
      • The electrons need to receive a certain threshold amount of energy to be freed from the metal and travel through the air.
    How can we tell if Planck was right?
      • What results would we expect if light behaves like a wave?
      • What about if it behaves like a packet of energy?
  • 20.
      • What results would we expect if light behaves like a wave?
      • What about if it behaves like a packet of energy?
      • If light behaves like a wave , then any frequency of light should be able to eject electrons if we dial up the amplitude of the wave (and therefore the intensity) high enough.
      • If light behaves like particles , then only frequencies higher than a certain threshold should eject electrons and produce current.
  • 21.
      • The light will behave like a wave : it will be possible to eject electrons at all frequencies .
      • The light will behave like particles : it will be possible to eject electrons only at frequencies higher than a threshold .
    Clicker Question: How do you think light will behave when we shine it on a metal?
  • 22. 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
  • 23. Post-Experiment Discussion Point: Does this finding change the wave-like observations we've made before?
  • 24. The photoelectric effects proves that light comes in discrete packets (photons)
    • Let’s think about waves first.
    • Imagine this fishing bobber.
    • What do we need to change about the wave to make the bobber go high enough to go through the ring?
  • 25. The photoelectric effects proves that light comes in discrete packets (photons)
    • Let’s think about waves first.
    • Now, instead thing about light shining on fluorescent molecules
    • Can bright light of any frequency excite the electron? NO
  • 26. Clicker question—photoelectric effect
    • Light is made up of particles (photons). The electrons can only absorb one whole photon at a time. If we have red and blue light of equal intensity, which of the following is true?
    • Red light will eject approximately ½ as many electrons as blue light
    • Blue light will eject way, way more electrons than red light
    • They will eject almost the same amount of electrons!
    Red photon energy Blue photon energy Photon energy = h * frequency Metal Air Energy
  • 27. Clicker question—photoelectric effect
    • Light is made up of particles (photons). The electrons can only absorb one whole photon at a time. If we have red and blue light of equal intensity, which of the following is true?
    • Red light will eject approximately ½ as many electrons as blue light
    • Blue light will eject way, way more electrons than red light
    • They will eject almost the same amount of electrons!
    Red photon energy Blue photon energy Photon energy = h * frequency Metal Air Energy
  • 28. Take-home message from all of this:
    • We can only understand the physics of light if it is both a wave and a particle . (Sorry!)
    Photoelectric effect Diffraction Interference Fluorescence
  • 29. Clicker Question--Electrons
    • Are electrons particles or waves?
    • Particles—duh!
    • Waves?
    • Both???
    • Neither
    • Yes
  • 30. Clicker Question--Electrons
    • Are electrons particles or waves?
    • Particles—duh!
    • Waves?
    • Both???
    • Neither
    • Yes
    It turns out that matter (electrons) behaves like waves and particles too!
  • 31. Well, if electrons can behave like waves…
    • Shouldn’t we be able to refract / focus the electrons?
    • Yes… ”Electron Microscopy!”
    http://www.columbia.edu/~ac558/jj1.jpg
  • 32. 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
  • 33. Next up is nuclear physics!! Homework problem Thin film interference in your kitchen Make your own videos / pictures!
    • Requires black coffee mug, dish soap, sunlight

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