Lect21_22_[Compatibility_Mode]

# Lect21_22_[Compatibility_Mode] - Physics 344 Foundations of...

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Physics 344 Foundations of 21 st Century Physics: Relativity, Quantum Mechanics and heir Applications Their Applications Instructor: Dr. Mark Haugan Office: PHYS 282 [email protected] TA: Dan Hartzler Office: PHYS 7 [email protected] Grader: Shuo Liu Office: PHYS 283 [email protected] Office Hours: If you have questions, just email us to make an ppointment. e enjoy talking about physics! appointment. We enjoy talking about physics! Reading: Carefully review chapter 23 in your Physics 272 textbook, Matter & Interactions Volume II, 2 nd edition.

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Question 1: A “staggering walker” has a probability of 1 in 3 of taking a 1 meter step in the x direction in any 5 second interval and a probability of 2 in 3 of taking no step. How far would you “expect” the walker to travel in an hour? A) 720 meters B) 360 meters C) 240 meters ) 160 meters D) 160 meters E) 120 meters Answer: 12 possible steps per minute implies 60x12 = 720 possible steps per hour. With a 1 in 3 chance of moving ahead 1 m for each possible step the single-step expectation value for the distance traveled is <dist/step> = 1m x (1/3) + 0m x (2/3) This implies an expected distance traveled for 720 steps 720 x <dist/step> = 240 m
Question 2: Which of these would be the most reasonable range values for you to expect the actual distance traveled in any given hour to fall? A) 240 ± 90 meters ) 240 0 meters B) 240 ± 60 meters C) 240 ± 15 meters D) 240 ± 5 meters E) 240 ± 1 meter nswer: e single- tep variance for this process is Answer: the single step variance for this process is σ 2 = [(1m) 2 x (1/3) + (0m) 2 x (2/3)] – 1m 2 /9 = 2m 2 /9 So, a reasonable estimate of the mean square deviation for N = 720 steps is 22 2 720 160 12.7 9 Nm m m σ =×=

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The Standard Model of Particle Physics Last lecture we took a closer look at the phenomenon of radioactive decay. This allowed us to introduce ideas about probability that play a central role in quantum physics, specifically expectation value and variance. We encountered radioactivity in the lecture before that while we quickly surveyed the origins of high-energy particle physics and of our present understanding of the structure of matter. In particular, we discussed the role that the discovery of radioactivity played in the emergence of the model of the nuclear atom, a model that you used throughout Physics 172 and 272. he detection of the neutron in 1932 put the final touch on this basic model The detection of the neutron in 1932 put the final touch on this basic model of matter, but the study of particle interactions in collisions with ever higher energies soon revealed many additional particles. Initially, these higher energy collisions were the result of natural processes, collisions between cosmic rays and atoms in the Earth’s upper atmosphere. The muons, pions and positrons that we have encountered in previous problems were all first discovered as products of such collisions.
Rather than trace the rest of the (complicated) history of the development of our present understanding of matter at the subatomic level, we will quickly

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## This note was uploaded on 11/26/2010 for the course PHYS 344 taught by Professor Garfinkel during the Spring '08 term at Purdue.

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Lect21_22_[Compatibility_Mode] - Physics 344 Foundations of...

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