# Lecture17 - Physics 344 Foundations of 21 st Century...

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Unformatted text preview: Physics 344 Foundations of 21 st Century Physics: Relativistic and Quantum Systems Instructor: Dr. Mark Haugan Office: PHYS 282 haugan@purdue.edu TA: Dan Hartzler Office: PHYS 7 dhartzle@purdue.edu Grader: Fan Chen Office: PHYS 222 chen926@purdue.edu Office Hours: If you have questions, just email us to make an appointment. We enjoy talking about physics! Help Session: Thursdays 2:00 4:00 in PHYS 154 Reading: Review Lecture Slides and Text Exam 1: Wednesday, October 5 at 8:00pm in WTHR 104 t x t=1sec t Q1. A spaceship traveling at 4 c /5 passes you at t = 0 seconds. One second later you fire a laser pulse after the ship. At what time, measured in your frame, does the pulse reach the ship? A) 8.0 seconds B) 6.0 seconds C) 5.5 seconds D) 5.0 seconds E) 4.5 seconds * Pulse worldline, x = t-1second Ship worldline, x = 4t/5 They cross when t-1second=4t/5 b t = 5 seconds Q2. If the ships frame is in standard orientation relative to yours, at what time does the pilot observe the pulses arrival? A) t = 3.0 seconds B) t = 4.0 seconds C) t = 5.0 seconds D) t = 6.0 seconds * The pilots coordinate time is simply the interval between the origin event and the reception event. The latter occurs at t = 5 seconds and x = Vt = 4 seconds, so, the arrival time is 2 2 5 4 3 seconds t =- = t x t x 1 A B C D E Q3. Which of the events plotted in this spacetime diagram is simultaneous with event 1 as measured in S ? Answer: event E Q4. Which of these events occurs earliest in S ? Answer: event D The Newtonian Limit and Galilean Relativity The idea that physics works the same way in all inertial frames, that is, the idea expressed by the Principle of Relativity, seems quite natural to us based on our everyday experiences. Even if you havent had the opportunity to notice that everything seems to work the same way on board a plane in level flight on a calm day, we know that our laboratory is moving in different ways at different times and we notice no differences in the outcomes of our experiments so long as the experiments are not sensitive to our relatively tiny acceleration and rate of rotation. Galileo first pointed this out as he was pondering the Copernican model of the Solar System. Galileo, Newton and others around at that time were not led immediately to special relativity by this insight, however. It turns out that there is another possible spacetime structure consistent with the principle of relativity and in which the fundamental concepts and principles of Newtonian physics, including p mv = a a are form invariant. Well show this and the sense in which special relativity has an approximate Newtonian limit, thus, explaining how we can find Newtonian concepts so natural even though they are, ultimately, wrong. When thinking about the Newtonian limit it is best to use conventional units. In such units the Lorentz transformation equations take the form ( 29 2...
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## This note was uploaded on 12/09/2011 for the course PHYS 344 taught by Professor Garfinkel during the Fall '08 term at Purdue University-West Lafayette.

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Lecture17 - Physics 344 Foundations of 21 st Century...

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