Phy107Spr07Lect19

# Phy107Spr07Lect19 - Homework Exam From last time Relativity H W 6 a s s ig n e d t h is a ft e rn o o n a t W ile y P lu s c o v e rs r e la t iv

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1 Phy107, Lect 19 1 Wed. Mar. 7, 2006 Hour Exam 2 : Wednesday, March 14 In-class, covering waves, electromagnetism, and relativity Twenty multiple-choice questions Will cover: Chap. 8, 9.1-9.3, 10 All lecture material You should bring 1 page notes, written double sided #2 Pencil and a Calculator Review Monday March 12 Review questions online under “Review Quizzes” link HW#6 assigned this afternoon at WileyPlus: covers relativity Homework & Exam Phy107, Lect 19 2 Wed. Mar. 7, 2006 From last time… Relativity! Simultaneity: events simultaneous in one frame will not be simultaneous in another. Proper time: t p Time interval measured in frame where events occur at same spatial location Time dilation: t= γ t p Time intervals in other frames longer by a factor γ (gamma, always bigger than 1) Phy107, Lect 19 3 Wed. Mar. 7, 2006 Traveling to the stars Spaceship leaves Earth, travels at 0.95c Spaceship later arrives at star 0.95 c 0.95 c d=4.3 light-years Phy107, Lect 19 4 Wed. Mar. 7, 2006 The ship observer’s frame ..then star arrives 0.95 c 0.95 c d=4.3 light-years Earth leaves… Phy107, Lect 19 5 Wed. Mar. 7, 2006 Question: proper time Both the astronaut and the earthling measure the time interval between leaving Earth and arriving at the star. Who measures the proper time? A. The astronaut B. The Earthling C. Both D. Neither Phy107, Lect 19 6 Wed. Mar. 7, 2006 " = 1 1 # ( v / c ) 2 = 1 1 # ( 0.95 ) 2 = 3.203 Speed of light v v Earth frame Rocket frame Both observers agree on relative speed, hence also gamma. Relative velocity of reference frames

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2 Phy107, Lect 19 7 Wed. Mar. 7, 2006 Total trip time Spaceship leaves Earth, travels at 0.95c 0.95 c d=4.3 light-years " t earth = d v c 95 . 0 years - light 3 . 4 = years 5 . 4 = Time for astronaut passes more slowly by a factor gamma. Trip time for astronaut is 4.5 yrs/3.2 = 1.4 years But this is not the proper time. Astronaut measures proper time. This time is longer than proper time by a factor gamma ( γ ) Phy107, Lect 19 8 Wed. Mar. 7, 2006 Some discrepancies?
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## This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

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Phy107Spr07Lect19 - Homework Exam From last time Relativity H W 6 a s s ig n e d t h is a ft e rn o o n a t W ile y P lu s c o v e rs r e la t iv

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