Spring 11 Phys 121 - HW 07

Spring 11 Phys 121 - HW 07 - dzifanu (sd26397) hw 7...

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Unformatted text preview: dzifanu (sd26397) hw 7 opyrchal (121102) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A battery with an emf of 7 . 8 V and internal resistance of 1 . 35 is connected across a load resistor R . If the current in the circuit is 1 . 2 A, what is the value of R ? Correct answer: 5 . 15 . Explanation: Let : E = 7 . 8 V , I = 1 . 2 A , and R i = 1 . 35 . The electromotive force E is given by E = I ( R + R i ) R = E I- R i = 7 . 8 V 1 . 2 A- 1 . 35 = 5 . 15 . 002 (part 2 of 2) 10.0 points What power is dissipated in the internal re- sistance of the battery? Correct answer: 1 . 944 W. Explanation: The power dissipation due to the internal resistance is P = I 2 R i = (1 . 2 A) 2 (1 . 35 ) = 1 . 944 W . 003 10.0 points Four resistors are connected as shown in the figure. 92 V S 1 c d a b 2 7 34 57 7 3 Find the resistance between points a and b . Correct answer: 16 . 201 . Explanation: E B S 1 c d a b R 1 R 2 R 3 R 4 Let : R 1 = 27 , R 2 = 34 , R 3 = 57 , R 4 = 73 , and E = 92 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 dzifanu (sd26397) hw 7 opyrchal (121102) 2 The series connection of R 2 and R 3 gives the equivalent resistance R 23 = R 2 + R 3 = 34 + 57 = 91 . 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 ) = (73 )[34 + 57 ] + (27 ) (73 ) + (27 ) [34 + 57 ] = 11071 2 , so the equivalent resistance is R ab = (27 ) (73 ) [34 + 57 ] (11071 2 ) = 16 . 201 . 004 (part 1 of 6) 10.0 points Consider the circuit in the figure. 13 . 4 V S 4 . 0 9 . 0 5 . 0 10 10 14 a) Find the current in the 5 . 0 resistor....
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Spring 11 Phys 121 - HW 07 - dzifanu (sd26397) hw 7...

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