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Chapter 12 Winter 2011

Chapter 12 Winter 2011 - Chapter 12 The Physical Properties...

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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 doesn’t 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 doesn’t 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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Chapter 12 Winter 2011 - Chapter 12 The Physical Properties...

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