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Unformatted text preview: Chapter 12 The Physical Properties of Matter Some notes for today: s Pick up a diffraction grating (the small, thin slides) in the boxes by the doors as you come in. s At the end of class, please return them to the boxes as you leave. The photoelectric effect (again and with too many words) s It was observed that light shining on a metal plate can eject electrons (make a current). s But there were only certain conditions under which it happened: f the light is too red, it will not happen no matter how If the light is too red, it will not happen no matter how much (amplitude) light gets shined on the metal. If the light is blue enough, even a very small amount (amplitude) of light will cause electrons to jump out of the metal. This can be interpreted in terms of frequency (or wavelength) for low frequencies (or long wavelengths), it doesnt work while for high frequencies (or short wavelengths) it does. Further, if we have blue enough light, a larger amplitude produces more electrons flying off the metal Increasing the frequency makes the electrons fly off faster . The photoelectric effect (again but with a picture) The photoelectric effect (a puzzle and an explanation) In terms of waves, this doesnt make sense. The energy of light should be associated with its amplitude. Regardless of the frequency, we should be able to wait it out and the energy in the metal (and of the electrons) should slowly increase until the electrons get ejected. Like turning the microwave on longer. And last two make no sense at all. Einstein suggested a radical explanation: The light was made up of tiny packets (quanta) of energy that depended on the frequency. When one of these packets hit an electron, it gave all its energy to the electron. If that energy (now kinetic energy of the electron) was enough, the electron could shoot out of the metal....
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This note was uploaded on 11/30/2011 for the course PHY S 100 taught by Professor Staff during the Winter '08 term at BYU.
- Winter '08