AP1200_Ch7_ModernPhysics-2008

AP1200_Ch7_ModernPhy - ModernPhysics thanknowledge AlbertEinstein History , Newtonianmechanics magnetism Lawsofthermodyna

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    Modern Physics Imagination is more important  than knowledge… Albert Einstein
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    History At the end of the 19 th  century, scientists believed that  they had learned almost everything about physics:  Newtonian mechanics Maxwell’s theories to unify electricity and  magnetism Laws of thermodynamics and kinetic theory But Classical physics fails to explain the behaviour of  matter on the atomic scale:  Blackbody radiation Photoelectric effect Emission of specific spectral lines from atoms
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    Development  Physics known at the end of the nineteenth century is  referred to as  classical physics .  The new physics  developed at the turn of the twentieth century is  called  modern physics . Major revolutions of physics in early 20 th  century: Einstein developed his  special theory of relativity Planck provided the basic ideas that led to the  birth of  quantum theory   New theories and their applications have led to many  important achievements.  
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    Special Theory of Relativity I The theory is based on: The relativity principle   the laws of physics are  the same in all inertial reference frames The principle of the constancy of the speed of light   the speed of light in empty space has the same  value in all inertial reference frames. The theory states that space & time are related;  and  mass and energy are convertible   E=mc 2 .    2 2 2 2 2 ) 1 / 1 1 ( c m c v c m mc KE o o - - = - = KE of a moving object: Total E of a moving object (PE=0): 4 2 2 2 2 c m c p E o + =
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    Special Theory of Relativity II According to the relativity theory: Time dilation   moving clocks are measured to  run slower: Length contraction   the length of a moving  object is measured to be shorter:  Mass increase    the mass of a moving body is  measured to increase with speed: e proper tim / 1 / 2 2 = - = o o t c v t t mass rest / 1 / 2 2 = - = o o m c v m m length proper / 1 2 2 = - = o o L c v L L
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    The Blackbody Radiation In 1900 Planck discovered a formula for blackbody  radiation that was  in complete agreement with experiment  data  at all wavelength.   ) 1 ( 2 ) , ( / 5 2 - = T k hc B e hc T I λ π Quantization of energy: nhf E n = Plank made two assumptions:  (a) the molecules can have  only discrete values of energy   (b) the molecules emit or  absorb energy in discrete packets called photons
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    Wave Particle Duality Waves as particles Photo electric effect Compton scattering Pair production Particles as waves de Broglie  wavelength Electron diffraction mC 2    =   E E    =  hf
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    The Photo Electric Effect Waves as Particles What is happening here? 
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This note was uploaded on 04/17/2011 for the course AP 1200 taught by Professor Michela.vanhove during the Spring '10 term at City University of Hong Kong.

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AP1200_Ch7_ModernPhy - ModernPhysics thanknowledge AlbertEinstein History , Newtonianmechanics magnetism Lawsofthermodyna

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