Lecture02 - 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! Reading: Sections 1.1 through 1.5 and Chapter 2 in Six Ideas that Shaped Physics, Unit R. Inertial Coordinate Systems Our prediction of how an electron moves through a particle accelerator and our consideration of ways to measure the electrons velocity after it exits the accelerator illustrated and emphasized the role that inertial coordinate systems play as we predict and observe what happens in the Universe. In previous courses, we have always used inertial coordinate systems to assign the x , y , z and t coordinate values that represent locations and times, which we then use to represent fundamental physics principles as we make predictions. Because the systems are inertial, free particle motions are represented by straight lines along which the particles move at constant speed. To compare an observed particle motion with a prediction of that motion, x(t) , y(t) and z(t) , we must have procedures to measure the x , y , z and t coordinates assigned to locations and times by the inertial coordinate system we used to make and to represent our prediction. The puzzle I left you with at the end of the first lecture and that we solved in recitation yesterday drew attention to the fact that measuring the t coordinate assigned an inertial coordinate system to the time at which an event happens requires a bit more care than we might have realized. The Puzzle Resolved To test the relativistic relationships among particle velocity, momentum and energy, some summer research students set out to measure the speed of electrons moving freely along a beam line after the electrons exit a particle accelerator with known momentum and energy. Their initial experimental proposal for doing this used three particle detectors spaced along the beam line and a single clock located right next to the second detector D2. Each detector emits a flash of light as an electron passes it and the clock records the time at which it receives the pulse emitted by each detector as an electron passes, accurate to 1 nanosecond. Label the times the clock records as an electron moves along the beam line T 1 , T 2 and T 3 . The students proposed to use the differences and and the distance D between detectors, measured by laying down rulers along the beam line, to determine the electrons speed. D1 D2 D3 C D = 30 meters D = 30 meters- v a 21 2 1 T T T =- 32 3 2 T T T =- predicted speed T 21 T 32 300 m/sec 0.099999900 sec 0.100000100 sec 0.6 c 0.67x10-7 sec 2.67x10-7 sec 0.8 c 0.25x10-7 sec 2.25x10-7 sec Since the electron moves freely and D1 and D2 are separated by the same distance as D2 and D3, the students expected to find...
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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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Lecture02 - Physics 344 Foundations of 21 st Century...

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