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Unformatted text preview: wright (daw2557) Chapter 27 de (14443) 1 This printout should have 7 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Four resistors are connected as shown in the figure. 97 V S 1 c d a b 1 8 47 54 7 1 Find the resistance between points a and b . Correct answer: 12 . 5721 . Explanation: E B S 1 c d a b R 1 R 2 R 3 R 4 Let : R 1 = 18 , R 2 = 47 , R 3 = 54 , R 4 = 71 , and E = 97 V . Ohms law is V = I R . A good rule of thumb is to eliminate junc tions connected by zero resistance. E B a d b c R 1 R 2 R 3 R 4 The series connection of R 2 and R 3 gives the equivalent resistance R 23 = R 2 + R 3 = 47 + 54 = 101 . The total resistance R ab between a and b can be obtained by calculating the resistance in the parallel combination of the resistors R 1 , R 4 , and R 23 ; i.e. , 1 R ab = 1 R 1 + 1 R 2 + R 3 + 1 R 4 = R 4 ( R 2 + R 3 ) + R 1 R 4 + R 1 ( R 2 + R 3 ) R 1 R 4 ( R 2 + R 3 ) R ab = R 1 R 4 ( R 2 + R 3 ) R 4 ( R 2 + R 3 ) + R 1 R 4 + R 1 ( R 2 + R 3 ) The denominator is R 4 ( R 2 + R 3 ) + R 1 R 4 + R 1 ( R 2 + R 3 ) = (71 )[47 + 54 ] + (18 ) (71 ) + (18 ) [47 + 54 ] = 10267 2 , so the equivalent resistance is R ab = (18 ) (71 ) [47 + 54 ] (10267 2 ) = 12 . 5721 ....
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 Spring '09
 SURESHSHARMA
 Physics

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