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Unformatted text preview: homework 06 FAUSAK, TAYLOR Due: Feb 25 2008, 4:00 am 1 Question 1, chap 28, sect 4. part 1 of 2 10 points A 28 V battery has an internal resistance r . 1 A 28 V r 42 56 internal resistance What is the value of r ? Correct answer: 4 (tolerance 1 %). Explanation: I 1 I 2 I 3 E r R 2 R 3 internal resistance Let : E = 28 V , R 2 = 42 , R 3 = 56 , and I 1 = 1 A . Since R 2 and R 3 are connected parallel, their equivalent resistance R 23 is 1 R 23 = 1 R 2 + 1 R 3 = R 3 + R 2 R 2 R 3 R 23 = R 2 R 3 R 2 + R 3 = (42 ) (56 ) 42 + 56 = 24 . Using Ohms law, we have E = I 1 r + I 1 R 23 r = E I 1 R 23 I 1 = 28 V (1 A) (24 ) 1 A = 28 24 = 4 . Question 2, chap 28, sect 4. part 2 of 2 10 points Determine the magnitude of the current through the 56 resistor on the righthand side of the circuit. Correct answer: 0 . 428571 A (tolerance 1 %). Explanation: The potential drop across the 56 resistor on the righthand side of the circuit is E 3 = E I 1 r = 28 V (1 A) (4 ) = 28 V 4 V = 24 V , so the current through the resistor is I 3 = E 3 r 3 = 24 V 56 = 3 7 A = 0 . 428571 A , and I 2 = I 1 I 3 = 1 A 3 7 A = 4 7 A = . 571429 A . Question 3, chap 28, sect 4. part 1 of 3 10 points 7 . 2 V 1 V 4 . 7 V I 1 1 . 3 2 I 2 7 . 7 I 3 9 . 7 homework 06 FAUSAK, TAYLOR Due: Feb 25 2008, 4:00 am 2 Find the current I 1 in the 1 . 3 resistor at the bottom of the circuit between the two power supplies. Correct answer: 0 . 734918 A (tolerance 1 %). Explanation: E 1 E 2 E 3 I 1 R A R B I 2 R C I 3 R D At a junction (Conservation of Charge) I 1 + I 2 I 3 = 0 . (1) Kirchhoffs law on the large outside loop gives ( R A + R B ) I 1 + R D I 3 = E 1 + E 2 . (2) Kirchhoffs law on the righthand small loop gives R C I 2 + R D I 3 = E 3 . (3) Let : R A = 1 . 3 , R B = 2 , R C = 7 . 7 , R D = 9 . 7 , E 1 = 7 . 2 V , E 2 = 1 V , and E 3 = 4 . 7 V . Using determinants, I 1 = vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle 1 1 E 1 + E 2 R D E 3 R C R D vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle 1 1 1 R A + R B R D R C R D vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle Expanding along the first row, the numera tor is D 1 = vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle 1 1 E 1 + E 2 R D E 3 R C R D vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle = 0 1 vextendsingle vextendsingle vextendsingle vextendsingle E 1 + E 2 R D E 3 R D vextendsingle vextendsingle vextendsingle vextendsingle + ( 1) vextendsingle vextendsingle vextendsingle vextendsingle E 1 + E 2 E 3 R C vextendsingle vextendsingle vextendsingle vextendsingle = [( E 1 + E 2 ) R D E 3 R D ] [ R C ( E 1 +...
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 Spring '07
 KBrowning

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