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Phy107Lect20 - HW#7 Chapter 11 Concept 2 6,14 20 32 34...

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Fri. Oct 22 Phy107 Lecture 20 Hour Exam 2 : Wednesday, Oct. 27 In-class (1300 Sterling Hall) Twenty multiple-choice questions Will cover: 8.1-8.6 (Light and E&M) 9.1-9.5 (E&M waves and color) 10, 11 (Relativity) You should bring Your student ID 1 page notes, written double sided – Calculator Pencil for marking answer sheet HW#7: Chapter 11 Concept: 2, 6,14, 20, 32, 34 Problems: 4, 6
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Fri. Oct 22 Phy107 Lecture 20 General Relativity and Gravity Special Relativity deals with inertial reference frames , frames moving with a constant relative velocity. It has some rather unusual predictions Time dilation Length contraction Mass-energy equivalence These were motivated by thought experiments based on simple postulates. General Relativity also motivated by some simple thoughts about gravity and free-fall.
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Fri. Oct 22 Phy107 Lecture 20 The Equivalence Principle Led Einstein to postulate the Equivalence Principle. Clip from Einstein Nova special.
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Fri. Oct 22 Phy107 Lecture 20 Equivalence principle Accelerating reference frames are indistinguishable from a gravitational force.
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Fri. Oct 22 Phy107 Lecture 20 Try some experiments Constant velocity Cannot do any experiment to distinguish accelerating frame from gravitational field t=0 t=t o t=2t o Floor accelerates upward to meet ball Constant accel. t=0 t=t o t=2t o
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Fri. Oct 22 Phy107 Lecture 20 Light follows the same path Path of light beam in our frame Velocity = v t =0 Velocity = v + at o t = t o Path of light beam in accelerating frame Velocity = v +2 at o t =2 t o
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Fri. Oct 22 Phy107 Lecture 20 Is light bent by gravity? If we can’t distinguish an accelerating reference frame from gravity… and light bends in an accelerating reference frame… then light must bend in a gravitational field But light doesn’t have any mass. How can gravity affect light?
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Fri. Oct 22 Phy107 Lecture 20 Light travels in a straight line In some ways, the path of light defines a straight line. Surveyors use laser to set heights. Can use a laser level to put up shelves. Seems to move in exactly a straight line. Maybe we are confused about what a straight line is
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Fri. Oct 22 Phy107 Lecture 20 What is a straight line? Claim that these are all straight lines
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Fri. Oct 22 Phy107 Lecture 20 Straight is shortest distance They are the shortest distances determined by wrapping string around a globe. On a globe, they are called ‘great circles’. In general, geodesics. This can be a general definition of straight, and is in fact an intuitive one on curved surfaces It is the one Einstein used for the path of all objects in curved space-time.
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