Lecture16

Lecture16 - 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 x t A B Clocks move along the worldlines shown and are used to measure the time that elapses between events A and B. Question 1: The clock(s) following which worldline(s) measure the spacetime interval between A and B? A) B) C) D) and E) none of them Question 2: The clock(s) following which worldline(s) measure the longest time interval between A and B? A) B) C) D) and E) none of them Question 3: The clock(s) following which worldline(s) measure the shortest time interval between A and B? A) B) C) D) and E) none of them synchronized * * * Question 4: A spaceship leaves Earth (event A) travels to a star 8 light-years away and then returns (event B) 20 yrs later. How much time elapses between events A and B as measured by the ships clock? Assume that the ship accelerates for a very short period of time while reversing course near the star so that it spends almost the entire trip traveling at constant speed. A) 20 yrs B) 16 yrs C) 12 yrs D) 10 yrs D) 8 yrs What are the Earth-frame components of the ships 4-velocity on the outward trip? x = 8 yrs t = 20 yrs Neglecting contributions from the short periods of accelerated motion, the outbound time lapse is approximately the interval between departure and turn-around, 2 2 100 64 6 out out out t x yr yr - =- = * ( / ) ( / ) (10 / 6) (8/ 6) (5/ 3) (4 / 3) out out out out out u t t x x t x t x = + = + = + The trip back takes the same amount of time. Question 5. Two photons of energy E are traveling away from each other in opposite directions. What is the mass of this 2-photon system? A) 0 B) E/2 C) E D) 2E 2 2 = 4 2 sys sys sys sys E E E E E P M P P E E - + = =- = * The mass of any system is its rest energy, its energy measured in a frame in which the systems momentum is zero....
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Lecture16 - Physics 344 Foundations of 21 st Century...

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