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Unformatted text preview: Solution for Homework 19 RL Circuits Solution to Homework Problem 19.1(Resistance Given Time Constant) Problem: A RL circuit has a time constant, , of 40s and an inductance, L, of 3H what is the resistance of the circiut? Select One of the Following: (a) (bAnswer) . 075 (c) 10 (d) 26 (e) 42 Solution The time constant for a RL circuit is defined by, = L R solve for R, R = L sustitute, R = 3 H 40 s evaluate, R = . 075 Total Points for Problem: 3 Points Solution to Homework Problem 19.2(Long/Short RL Problem) Problem: A coil of resistance 12 and selfinductance 2mH is connected across an ideal 12V battery. (a)What is the initial current? Select One of the Following: (aAnswer) 0A (b) 1A (c) 144A (d) . 024A (e) 6000A (b)What is the final current? Select One of the Following: 1 (a) 0A (bAnswer) 1A (c) 144A (d) . 024A (e) 6000A Solution to Part(a) When the circuit is first connected, the inductor allows zero initial current flow, I (0) = 0 , since an inductor resists changes in current and does not allow instantaneous changes in current. Grading Key: Part (a) 2 Points Solution to Part(b) After a long time, I is not changing, so V L = dI dt = 0 , and substituting into the loop equation, V battery IR = , gives I = V battery R = 1 A. Grading Key: Part (b) 2 Points Total Points for Problem: 4 Points Solution to Homework Problem 19.3(Magnetic Field of Two WIres) Problem: Two infinite straight wires carry current I = 2A as shown below. One wire is parallel to the y axis and one wire is parallel to the z axis. The current directions are as drawn. The distance from each wire to point P is 3cm . Calculate the magnetic field at point P . Be sure to report the magnetic field as a vector. Select One of the Following: (a) 2 . 4 10 5 Ty + 2 . 4 10 5 T z (b) 1 . 3 10 5 Tx 1 . 3 10 5 Ty (c) 2 . 4 10 5 Ty 2 . 4 10 5 T z (dAnswer) 1 . 3 10 5 Ty 1 . 3 10 5 T z (e) 2 I d d x y I P Wire 1 Wire 2 Solution (a) The field of an infinite wire: The field of on infinite wire is given by B = I 2 R R is the same for both wire one and wire two. The direction can be read off using the righthand rule. (b) Compute the field of wire one: vector B 1 = I 2 R = (4 10 7 Tm A )(2A) 2 (0 . 03m) = 1 . 3 10 5 Ty (Correct Sig Figs) (c) Compute the field of wire two : vector B 2 = I 2 R = (4 10 7 Tm A )(2A) 2 (0 . 03m) = 1 . 3 10 5 T z (Correct Sig Figs) (d) Compute the total field: The total field is the vector sum of the two vector B tot = vector B 1 + vector B 2 = 1 . 3 10 5 Ty 1 . 3 10 5 T z Total Points for Problem: 3 Points Solution to Homework Problem 19.4(Velocity of Alpha Particle) 3 Problem: An alpha particle is a Helium nucleus and has twice the charge, q = 2 q p , and four times the mass, m = 4 m p , of a proton (the mass of a proton is...
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This note was uploaded on 03/29/2010 for the course PHYS 2469 taught by Professor Stewat during the Spring '10 term at University of Arkansas Community College at Batesville.
 Spring '10
 Stewat
 Inductance, Resistance, Work

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