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Blackbody Radiation

Blackbody Radiation. Ultraviolet Catastrophe. 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.

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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?

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