RealExam2 - Physics 21 Fall, 2004 1 2 3 4 5 Total Name:...

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Physics 21 Fall, 2004 Hour Exam #2 1 2 3 4 5 Total Name: Recitation Time Recitation Leader Nov. 2, 2004 This exam is closed notes and closed book. You must show enough work on all problems to convince the grader you understand how to solve the problem. You may use a calculator. An equation sheet is on the last page. There are fve problems; each counts 20 points. The points For each problem are divided approximately equally among the parts (a), (b), etc. Problem 1. ±or the Following circuit: R L C V rms ( frequency ω ) (a) Write the loop equation For this circuit. (b) Draw a phasor diagram For this circuit, and use it to fnd an expression For the phase angle φ in terms oF R , L ,and C ω . (c) IF R =3 . 00 Ω, L =5 . 00 mH, and C =1 . 25 m±, what angular Frequency ω gives the maximum rms current For a fxed V rms ? What is the value oF φ at this Frequency? (d) IF the ac power source is turned o², how long does it take the oscillating current to diminish to 25% oF its steady state value? Use the values oF R , L , and C given in part (c).
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Problem 2. An electron with velocity v passes unde- flected through a region where there are uniform elec- tric and magnetic Felds. The components of v are v x = 2 m/s, v y = 3 m/s, and v z = 4 m/s. B is in the x direction: B x = B 0 =0 . 1T , B y = B z =0. (a) ±ind the electric Feld E . (b) If the electric Feld is turned o², the electron will follow a helical path. ±ind the components v ± and v of the electron’s velocity parallel and perpen- dicular to B . (c) Start with F = m e a and show that the radius of the helical motion is given by r = m e v eB 0 Hint: Centrifugal acceleration is v 2 /r .
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This note was uploaded on 08/06/2008 for the course PHYS 21 taught by Professor Hickman during the Fall '07 term at Lehigh University .

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RealExam2 - Physics 21 Fall, 2004 1 2 3 4 5 Total Name:...

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