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Blackbody Radiation

Blackbody Radiation

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Blackbody Radiation

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  1. Blackbody Radiation Ultraviolet Catastrophe

  2. Max Planck, Planck’s constant • Found an empirical formula which fit the measured blackbody curve • Looked for way to derive this empirical formula Max Karl Ernst Ludwig Planck Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html

  3. Max Planck, Planck’s constant so... Light is a Particle! wait a minute... Light is a Wave! Max Karl Ernst Ludwig Planck Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html

  4. Disclaimer . . .

  5. What did Einstein Win his Nobel Prize for? photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg

  6. The Photoelectric Effect

  7. Photoelectric Effect Intuition • What would a plot of current vs. light intensity look like? • What would a plot of current vs. voltage look like? • What would a plot of threshold voltage vs. light frequency look like?

  8. WHAT BROUGHT DOWN THE NEPHITES 200 years of peace after Christ's visit. • Began to be Lamanites • Costly Apparel • Churches built to get gain • Persecuted prophets who were doing miracles • Willful rejection of good

  9. The Photoelectric Effect

  10. The Photoelectric Effect

  11. Wave Theory of Light and the Photoelectric Effect Existence of a threshold voltage Current increases with intensity Threshold is a function of light frequency No intensity threshold No time delay Fairly monochromatic electron energies

  12. Einstein’s Explanation... Plank was right! photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg

  13. Photons and Work Functions

  14. Light is incident on a Zinc plate (Φ=4.31 eV). Only one of the following lights will cause the electrons to be emitted from the surface, which one is it. • Infra-red • Visible • Ultra-violet

  15. What is the velocity of the electrons coming off the metal?

  16. A beam of ultra violet light is incident on the metal ball of an electroscope (hf > Φ) that is initially negatively charged. The electroscope . . . Losses its negative charge.

  17. A beam of visible light is incident on the metal ball of an electroscope (hf < Φ) that is initially negatively charged. The electroscope . . Nothing happens—even after a long time.

  18. Why does UV light give you a sunburn?

  19. Discussion question: 400-nm wavelength light strikes a metal surface, a stream of electrons emerges from the metal. If the intensity of the light striking the surface is doubled, • More electrons are emitted in a given time interval. • The electrons that are emitted are more energetic. • Both of the above • Neither of the above

  20. Discussion question: When 400-nm wavelength light strikes a metal surface, a stream of electrons emerges from the metal. If the 400-nm light is replaced with 300 nm and the lamp is adjusted so that the intensity of the light striking the surface is the same as it was for the 400-nm light. With the 300-nm light, • More electrons are emitted in a given time interval. • The electrons that are emitted are more energetic. • Both of the above • Neither of the above

  21. Discussion question: A beam of ultra-violet light is incident on the metal ball of an electroscope that is initially uncharged. Does the electroscope acquire a charge? • Yes, it acquires a positive charge. • Yes, it acquires a negative charge. • No, it does not acquire a charge.

  22. Double Slit Interference

  23. Single Photon Interference

  24. X-Ray Tube

  25. In the Compton experiment, the wavelength of the scattered light is ______________ the wavelength of the incident light. • Longer than • The same as • Shorter than

  26. Compton Scattering of a “Photon” Before After e- e- Are you pondering what I’m pondering? Yes, but how will we ever get that many rubber bands? No you buffoon! Why do you need x-rays to see this?