2010 PHYSICS 002C Lecture 21

2010 PHYSICS 002C Lecture 21 - PHYSICS 002C Lecture 21 May...

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1 PHYSICS 002C Lecture 21 May 17, 2010 Serway and Jewett Chapter 28.1-4 – Quantum Mechanics Q. To explain the spectrum of black body radiation Max Planck in 1900 hypothesized that the possible energies of an oscillator are a) exact; b) differentiable; c) indefinite; d) quantized; e) invariant. Q. To explain the photoelectric effect discovered by Hertz, Albert Einstrein in 1905 hypothesized that light of density d , energy e , frequency f , Gibbs potential g , and intensity i is emitted and absorbed in quantized units called photons having energy a) hd ; b) he ; c) hf ; d) hg ; e) hi . Q. In 1923 A. H. Compton showed experimentally that x-rays scattered from electrons like a) waves; b) ripplons; c) pinticles ; d) pustibules ; e) particles. Chap 28.4 Prelude to quantum physics – What is a wave? What is a particle? A wave is a propagating disturbance of some kind that transmits energy and momentum. Standing waves have only energy. If the wave is in a material medium such as water or air or earth or even fire (a plasma) [the four elements of yore], the parts of the medium move to & fro but have no net movement associated with the wave. A particle is an idealization of a material object such as a marble, a baseball, a planet, star, or galaxy, in which we ignore all parameters except e.g. the center of mass coordinate and the mass, plus possibly the charge, the velocity, and sometimes the angular momentum associated with its spin. Euclid’s notion of a “point” is “that which has no extent”. The concepts of mass points and continuous waves do not work perfectly, and are bad descriptions of light and atoms, and even under some circumstances for large objects such as buckyballs and tubs of liquid helium. Little massive objects such as electrons and massless ones such as the particles of light that we call photons both exhibit Point interactions Interference effects So they are both point-like and wave-like. To understand means to be able to predict the course of events from an initial set of circumstances, as in understand the stock market or understand why someone would behave in a certain way. So we can say we understand the behavior of small things in terms of the axioms of quantum mechanics. Even so, we cannot be blamed for exhibiting our stupidity by asking WHY is this the way the world works? WHAT is the underlying machinery of it?
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2 What was wrong with the old physics wasn’t that hard enough? I will ignore that comment and proceed to
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This note was uploaded on 09/23/2010 for the course PH 02c taught by Professor Mile during the Spring '04 term at Riverside Community College.

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2010 PHYSICS 002C Lecture 21 - PHYSICS 002C Lecture 21 May...

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