2061x2_solutions_sp03

2061x2_solutions_sp03 - PHY2061 R. D. Field PHY 2061 Exam 2...

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PHY2061 R. D. Field Exam 2 Solutions Page 1 of 7 March 27, 2003 PHY 2061 Exam 2 Solutions Problem 1 (20 points): Circle true or false for following (2 points each). (a) (True or False) The speed of light in a vacuum is independent of the velocity of the source of the light, but depends on the velocity of the observer. (b) (True or False) The magnetic force cannot change the speed of a charged particle. (c) (True or False) The magnetic field produced by a moving charged particle is perpendicular to the velocity of the particle. (d) (True or False) The magnetic force on a charged particle is perpendicular to the velocity of the particle. (e) (True or False) The mass and charge of a particle depends on its speed. (f) (True or False) There can be no electric or magnetic force on an electrically neutral wire. (g) (True or False) Magnetic field lines are always perpendicular to electric field lines. (h) (True or False) The vector function y y x x y x B ˆ ˆ ) , ( + = r represents a possible magnetic field with magnitude given by 2 2 ) , ( y x y x B + = . (i) (True or False) The total net magnetic flux through any closed surface is always zero. (j) (True or False) Electric and magnetic fields are massless, but contain energy.
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PHY2061 R. D. Field Exam 2 Solutions Page 2 of 7 March 27, 2003 Problem 2 (relativity, 20 points): Protons leave a particle accelerator with a speed of v = 0.75c to enter and travel through an evacuated tube that is at rest in the laboratory and is 9 m long, as measured by an observer in the laboratory, and then finally reach a detector. (Note: c = 3.0x10 8 m/s) Part A (5 points): How long does it take for a proton to travel from one end of the tube to the other ( in nanoseconds ) according to an observer in the laboratory frame? Answer: 40 Solution: In any frame, distance equals speed times time and hence ns s s m m v d t 40 10 4 ) / 10 3 ( 75 . 0 9 8 8 = × = × = = . Part B (6 points): How long does it take for a proton to travel from one end of the tube to the other ( in nanoseconds ) according to an observer traveling with a proton? Answer: 26.5 Solution: The proton frame is the proper time and hence ns ns t t 5 . 26 512 . 1 40 = = = = γ τ , where I used 512 . 1 1 / 1 2 = = β . Part C (5 points): What is the tube’s length ( in m ) as measured by an observer traveling with a proton?
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This note was uploaded on 05/31/2011 for the course PHY 2061 taught by Professor Fry during the Spring '08 term at University of Florida.

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2061x2_solutions_sp03 - PHY2061 R. D. Field PHY 2061 Exam 2...

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