CHASE_HR38_stdt - 1 Chapter 38 The sub-atomic world behaves...

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Unformatted text preview: 1 Chapter 38 The sub-atomic world behaves very differently from the world of our ordinary experiences. Quantum physics deals with this strange world and has successfully answered many questions in the sub-atomic world, such as: Why do stars shine? Why do elements order into a periodic table? How do we manipulate charges in semiconductors and metals to make transistors and other microelectronic devices? Why does copper conduct electricity but glass does not? Things on a very small scale behave like nothing that you have any direct experience with. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seenit is very difficult to get used to and it appears peculiar and mysterious to everyone, both to the novice and the experienced physicist. Even the experts do not understand it the way they would like to, and it is perfectly reasonable that they should not, because all of direct, human experience and human intuition applies to large objects. We know how large objects will act, but things on a small scale just do not act that way. Richard Feynman Photons and Matter Waves 38- 2 Quantum physics: Study of the microscopic world Many physical quantities found only in certain minimum (elementary) amounts, or integer multiples of those elementary amounts These quantities are "quantized" Elementary amount associated with this a quantity is called a "quantum" (quanta plural) Analogy example: 1 cent or $0.01 is the quantum of U.S. currency Electromagnetic radiation (light) is also quantized, with quanta called photons. This means that light is divided into integer number of elementary packets (photons). The Photon, the Quantum of Light 38- 3 The energy of light with frequency f must be an integer multiple of hf . In the previous chapters we dealt with such large quantities of light, that individual photons were not distinguishable. Modern experiments can be performed with single photons. So what aspect of light is quantized? Frequency and wavelength still can be any value and are continuously variable, not quantized The Photon, the Quantum of Light, cont'd 38- (photon energy) E hf = c f = However, given light of a particular frequency, the total energy of that radiation is quantized with an elementary amount (quantum) of energy E given by: Where the Planck constant h has a value: 34 15 6.63 10 J s 4.14 10 eV s h-- = = where c is the speed of light 3x10 8 m/s 4 38- Checkpoint 1 A) yellow light from a sodium vapor lamp B) gamma ray emitted by a radioactive nucleus C) radio wave emitted by the antenna of a commercial radio station D) microwave beam emitted by airport traffic control radar 1. Which photon has the highest energy?...
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This note was uploaded on 06/11/2010 for the course PHYSICS 207 taught by Professor Ellis during the Spring '10 term at SUNY Buffalo.

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CHASE_HR38_stdt - 1 Chapter 38 The sub-atomic world behaves...

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