Week 6 - FIRST YEAR PHYSICS FIRST YEAR PHYSICS PHYS142...

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Unformatted text preview: FIRST YEAR PHYSICS FIRST YEAR PHYSICS PHYS142 & 143 LECTURER: Dr. Carey Freeth Rm 4.110 Ph. 02 42214798 Email: carey_freeth@uow.edu.au MODERN PHYSICS MODERN PHYSICS Introduction The physics of the nineteenth Century and before is called classical physics. Mechanics was known to Newton and Galileo (although not all the discoveries had been made) and the laws of electromagnetism are essentially unchanged (just as are the laws of mechanics in our everyday world). However, at the end of the 19th. century there existed a number of observations which could not be explained by the existing laws of mechanics and electromagnetism. (Blackbody radiation, photoelectric effect, spectral lines of hydrogen etc.). Classical physics was in a turmoil and fundamental laws and concepts had to changed to explain the observed phenomena. MODERN PHYSICS MODERN PHYSICS The Architects of Modern Physics The Fifth International Congress of Physics Solvay Institute Brussels 1927 In Modern Physics, we introduce the concepts developed in the 20th. Century to "explain" or describe the physical world as we know it. Emphasis is placed on those phenomena and discoveries which cannot be explained in the frame work of classical physics. For example, the foundations of our understanding of atomic and nuclear structure lie in the two great ideas of Modern Physics, relativity theory and quantum theory. The applicability of "Modern" and classical physics is shown in the following diagram. ELECTRICITY MAGNETISM LIGHT HEAT MECHANICS ELECTROMAGNETISM ELECTROMAGNETIC RADIATION X-RAYS SPECTRA NUCLEUS RADIOACTIVITY RELATIVITY WAVE PARTICLE DUALITY ELECTRON QUANTUM ELECTRONIC STRUCTURE ATOM SOLIDS MOLECULES MASS ENERGY QUANTUM FIELD CLASSICAL QUANTUM RELATIVISTIC QUANTUM WAVE MECHANICS Special Theory of Relativity The theory of special relativity was developed by Albert Einstein in 1905, and is fundamental to all modern physics. However, the idea of relativity existed before Einstein and was embodied in Newtonian Mechanics. The Laws of Classical Mechanics were known to be invariant in all inertial systems i.e. reference frames traveling with constant velocity relative to each other. This, in fact, was required by the relativity principle of classical mechanics. Special Theory of Relativity A light pulse is sent out by a person on the train. According to Galilean relativity , the speed of the pulse = c + v relative to a stationary observer s. Co-ordinate transformations between two such systems, S and S', are given by: (i.e. Universal time - foundation of Newtonian mechanics - assumes that both observers see the event simultaneously). These are called the Galilean Co-ordinate transformations....
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Week 6 - FIRST YEAR PHYSICS FIRST YEAR PHYSICS PHYS142...

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