Physhw 8-solutions (1)

Physhw 8-solutions (1) - billing (cab4763) hw 8 opyrchal...

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Unformatted text preview: billing (cab4763) hw 8 opyrchal (121104) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 3) 10.0 points 22 . 9 4 . 29 18 . 1 27 . 9 V 13 . 95 V Find the current through the 18 . 1 (lower) resistor. Correct answer: 0 . 743836 A. Explanation: r 1 r 2 R E 1 E 2 I 1 I 2 I 3 Let : E 1 = 27 . 9 V , E 1 = 13 . 95 V , r 1 = 22 . 9 , r 2 = 4 . 29 , and R = 18 . 1 . Assuming currents I 1 , I 2 , and I 3 in the direction show, we get I 3 = I 1 + I 2 . Applying Kirchhoffs loop rule, we can get two equations. E 1 = I 1 r 1 + I 3 R (1) E 2 = I 2 r 2 + I 3 R = ( I 3- I 1 ) r 2 + I 3 R =- I 1 r 2 + I 3 ( R + r 2 ) , (2) Multiplying Eq. (1) by r 2 , Eq. (2) by r 1 , E 1 r 2 = I 1 r 1 r 2 + r 2 I 3 R E 2 r 1 =- I 1 r 1 r 2 + I 3 r 1 ( R + r 2 ) Adding, E 1 r 2 + E 2 r 1 = I 3 [ r 2 R + r 1 ( R + r 2 )] I 3 = E 1 r 2 + E 2 r 1 r 2 R + r 1 ( R + r 2 ) = (27 . 9 V) (4 . 29 ) + (13 . 95 V) (22 . 9 ) (4 . 29 ) (18 . 1 ) + (22 . 9 ) (18 . 1 + 4 . 29 ) = . 743836 A . 002 (part 2 of 3) 10.0 points Determine the current in the 22 . 9 (upper) resistor. Correct answer: 0 . 630418 A. Explanation: From (1), get I 1 = E 1- I 3 R r 1 = 27 . 9 V- (0 . 743836 A) (18 . 1 ) 22 . 9 = . 630418 A . 003 (part 3 of 3) 10.0 points Determine the current in the 4 . 29 (middle) resistor. Correct answer: 0 . 113419 A. Explanation: From (2), get I 2 = E 2- I 3 R r 2 = 13 . 95 V- (0 . 743836 A) (18 . 1 ) 4 . 29 = . 113419 A . billing (cab4763) hw 8 opyrchal (121104) 2 004 (part 1 of 2) 10.0 points The circuit has been connected as shown in the figure for a long time. 12 V S 11 F 2 2 8 4 4 4 What is the magnitude of the electric po- tential across the capacitor? Correct answer: 4 V. Explanation: E S 1 C t b a b I t R 1 I t R 2 I b R 3 I b R 4 Let : R 1 = 20 , R 2 = 28 , R 3 = 4 , R 4 = 44 , and C = 11 F ....
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This note was uploaded on 03/25/2011 for the course PHYSICS 121 taught by Professor Fayngold during the Spring '10 term at NJIT.

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Physhw 8-solutions (1) - billing (cab4763) hw 8 opyrchal...

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