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Catch up and Test Review

# Catch up and Test Review - Announcements New homework set...

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Announcements New homework set is due tomorrow at 10 AM I’m trying to identify all clickers used in the class; that’s why I’ve been sending out emails so I can associate the points for each clicker with the appropriate student if you have used a clicker, those scores have been recorded Exam this Thursday on thermodynamics, electricity and magnetism and (some) special relativity (no general relativity) as for the first exam, you can bring one sheet of notes review, the 2 nd half of this lecture

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Special relativity The special theory of relativity can be summarized with two precepts Some of the consequences are not so intuitive slowing down of clocks lengths contracting masses increasing The laws of physics are the same in all coordinate systems either at rest or moving at constant speed with respect to one another The speed of light in a vacuum has the same value regardless of the velocity of the observer or the velocity of the source emitting the light
All is not well with Galilean relativity Speed of light is supposed to have one value in vacuum 3 X 10 8 m/s …or more precisely 2.99792458 X 10 8 m/s But consider the gedanken experiment to the right The observer inside a railway car (S’) travelling at a velocity v shines a flashlight He measures the light beam as travelling at c (3X10 8 m/s) The woman S standing by the side of the track measures the speed of light at what value? Common sense says c+v. But if the answer is c+v, then Maxwell’s description of electricity and magnetism is not right, because he said (and his equations demonstrated)that light can only travel at the speed of light.

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Ether drift and Fitzgerald and Lorentz In 1882, 2 physicists, G.F. Fitzgerald and H.A. Lorentz, suggested a solution to problem posed by Michelson- Morley experiment Fitzgerald: moving through ether generates a resisting force which compresses apparatus 1/2 millionth of 1 percent enough to explain lack of measureable ether drift caused by Earths motion through the ether Lorentz was looking for transformation equations between inertial frames of reference that would leave electromagnetic forces invariant Same transformation as found by Fitzgerald; interesting consequences moving objects would contract time would slow down Poincare also pointed out that mass would increase with speed and that the maximum speed for any object would be the speed of light
Albert Einstein, again All of the previous ideas are in Einstein’s theory of special relativity Significance of Einstein’s work is that he was able to show simply and directly that they were natural consequences of a profound and insightful reexamination of some basic assumptions about nature of physical measurements Circumstances at beginning of 20th century similar to those at time of Newton Several physicists were close to making a breakthrough but only one (Newton, Einstein) able to

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Catch up and Test Review - Announcements New homework set...

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