hw6sol - Flores, Michael Homework 6 Due: Mar 1 2004, 4:00...

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Unformatted text preview: Flores, Michael Homework 6 Due: Mar 1 2004, 4:00 am Inst: Sonia Paban 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page find all choices before making your selection. The due time is Central time. 001 (part 1 of 1) 10 points If the emf of a battery is 23 V and a current of 39 A is measured when the battery is shorted, what is the internal resistance of the battery? Correct answer: 0 . 589744 . Explanation: Given : E = 23 V and I = 39 A . When the battery with an emf E is shorted, with current I flowing, the internal resistance R i is R i = E I = 23 V 39 A = 0 . 589744 . 002 (part 1 of 2) 10 points Consider the following two cases. case a: 3 A 3 A = 19 19 R a case b: 3 A 3 A = 19 19 R b Find the ratio of dissipated powers, P a P b . 1. P a P b = 1 2. P a P b = 1 2 3. P a P b = 1 4 correct 4. P a P b = 1 8 5. P a P b = 2 6. P a P b = 8 7. P a P b = 4 Explanation: Given : R 1 = R 2 = R = 19 and I = 3 A . In case a, the two resistors are parallel, so the total resistance is 1 R a = 1 R 1 + 1 R 2 = R 2 + R 1 R 1 R 2 R a = R 1 R 2 R 1 + R 2 = R 2 . In case b, the two resistors are in series, so the total resistance is given by R b = R 1 + R 2 = 2 R. P a = I 2 R a = 1 2 I 2 R P b = I 2 R b = 2 I 2 R = P a P b = 1 2 I 2 R 2 I 2 R = 1 4 . 003 (part 2 of 2) 10 points Find P a . Correct answer: 85 . 5 W. Explanation: P a = 1 2 I 2 R = 1 2 (3 A) 2 (19 ) = 85 . 5 W . 004 (part 1 of 1) 10 points Consider the circuit 21 . 7 43 . 4 4 3 . 4 21 . 7 43 . 4 a b Flores, Michael Homework 6 Due: Mar 1 2004, 4:00 am Inst: Sonia Paban 2 What is the equivalent resistance between the points a and b ? Correct answer: 37 . 975 . Explanation: Given : R 1 = R = 21 . 7 , R 2 = 2 R = 43 . 4 , R 3 = 2 R = 43 . 4 , R 4 = R = 21 . 7 , and R 5 = 2 R = 43 . 4 . R 1 R 2 R 3 R 4 R 5 a b c d The circuit is redrawn below. R 1 = R R 3 = 2 R R 2 = 2 R R 4 = R R 5 = 2 R a b c d Basic Concepts: R series = R 1 + R 2 + R 3 + 1 R parallel = 1 R 1 + 1 R 2 + 1 R 3 + Solution: This circuit can be analyzed by straight-forward series/parallel analysis: R 4 and R 5 are in series, so R 45 = R + 2 R = 3 R . R 2 and R 3 are in parallel with R 45 , so 1 R 2345 = 1 2 R + 1 2 R + 1 3 R = 8 6 R R 2345 = 3 R 4 . R 1 and R 2345 are in series, so R eq = R + 3 R 4 = 7 R 4 = 7 (21 . 7 ) 4 = 37 . 975 . 005 (part 1 of 4) 10 points Twelve resistors, each of equal value R = 2 . 9 , are connected so that each is along one edge of a cube, as shown in the figure. A current of I = 9 . 1 A is introduced at point a. The current will be allowed to exit only along a wire at point b, as drawn....
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hw6sol - Flores, Michael Homework 6 Due: Mar 1 2004, 4:00...

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