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SMDEP Physics

SMDEP Physics. Today: Electromagnetic Radiation Quantum nature of light, electrons Tomorrow: Astronomy, Extrasolar planets, Cosmology, Dark Matter, Dark Energy, Black Holes and more http://www.astro.yale.edu/krines/smdep. Test Results. Mean = 20.4/37 (max:33) Median = 20 Stddev = 5.6

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SMDEP Physics

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  1. SMDEP Physics Today: Electromagnetic Radiation Quantum nature of light, electrons Tomorrow: Astronomy, Extrasolar planets, Cosmology, Dark Matter, Dark Energy, Black Holes and more http://www.astro.yale.edu/krines/smdep

  2. Test Results • Mean = 20.4/37 (max:33) • Median = 20 • Stddev = 5.6 • CLASS PARTICIPATION AND HW • Homework: 36 possible, mean: 26, max:34 • Bonus HW: 22 possible, mean: 16, max:22 • Group revotes: 36 possible, mean: 20, max: 30 • Total of above: 94 possible, mean: 62, max: 81

  3. This Test and the MCAT • Yesterday’s test: • 60 minutes, 37 questions • No calculators • MCAT (Paper) • 50 minutes, 37 questions • (Total of 100 minutes for 37 physics questions, 40 chemistry questions) • No calculators • This course covered 80% of the questions in online practice exam • MCAT (Computer) • About 30% fewer questions and 30% less time

  4. MCAT Suggestions • Practice, practice, practice • Practice exams are the best preparation • Improves test-taking speed • Questions (or variations) repeat • Review results of practice tests • Know sin/cos of 0,30,45,60,90 • Know how to approximate square roots • Estimate numbers only to precision needed to identify correct answer • Princeton Review courses, books (ebay)

  5. Dinosaur Group Winners • Velociraptor • Nkem Ezeamama • James Nelson • Kia Hope Shine • Runners-up: • Allosaurus • Iguanodon • Deinonychus • Apatosaurus

  6. Planet Group Winners • Europa • Roy Emanuel • DJ Lewis • James Nelson • Runners-up: • Uranus • Callisto • Neptune • Venus

  7. Individual Point Leaders • Required HW: • Khalilah Daley • Nkem Ezeamama • Leena Nguyen • Brett Thomas • Bonus HW: • Chineme Enyioha • Bryan Greer • Kia Hope Shine • Group Revotes: • Gaby Cobos • DJ Lewis • Participation total: • Nkem Ezeamama • DJ Lewis

  8. Next Year • KR moving to Boston • New email: krines@cfa.harvard.edu • SMDEP Physics webpage to end (move?) • Full-time research, so please email for help with physics courses • Open invite: • If you’re in Boston, I’ll take you out to lunch • Email ahead of time

  9. Nature of Light • Behavior of light with mirrors and lenses suggests it behaves like particles • If light were made up of particles, what would happen in the single-slit and double-slit experiments? • Diffraction and two-slit interference are properties of waves -> light has wavelike nature

  10. Nature of Light • Photoelectric effect: • Shine (monochromatic) light at “broken circuit”, light frees electrons so current flows • If light is wavelike, can generate current with high-intensity, low-frequency light • Current depends on intensity, not frequency • If light is particle-like, only increase in frequency changes photoelectric effect • Below threshold frequency, no photons have enough energy to start current (at any intensity) • Experiments show that light must come in discrete packets of energy -> particle-like behavior

  11. Nature of Light • What if you could slow down the emission rate from a photon source so that there was one photon at a time? • Double-slit experiment • Does a photon interfere with itself??? • Photon must be in multiple locations at once • Photon is “probability packet” in space

  12. Nature of Light • Wave-particle duality • Double-slit experiment shows wave properties • Photoelectric effect shows particle properties • Single-photon double-slit experiment shows both wave and particle properties! • If you cover one slit, no interference pattern • (Still shows single-slit diffraction pattern) • Photon is “probability packet” in space

  13. Nature of Elementary ‘Particles’ • Electrons found only in discrete “orbits” around nuclei • Can think of electrons as standing waves • What if you could slow down the emission rate from an electron source so that there was one electron at a time? • Double-slit experiment • Does an electron interfere with itself???

  14. 10 0 of 5 You have four lasers which emit light of different colors. Which laser emits photons with the largest wavelength? • Red • Green • Blue • Yellow • Need more info

  15. 10 0 of 5 You have four lasers which emit light of different colors. Which laser emits photons with the largest energy? • Red • Green • Blue • Yellow • Need more info

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