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Unformatted text preview: hopkins (tlh982) HW 05 criss (4908) 1 This printout should have 23 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 3 . 1 cm length of tungsten filament in a small lightbulb has a resistance of 0 . 031 . Find its diameter. (The resistivity is 5 . 6 10 8 m). Correct answer: 0 . 267023 mm. Explanation: Let : L = 3 . 1 cm = 0 . 031 m , R = 0 . 031 , and = 5 . 6 10 8 m . Resistance is R = L A = L parenleftbigg d 2 parenrightbigg 2 = 4 L d 2 , d = radicalbigg 4 L R = radicalBigg 4 (5 . 6 10 8 m) (0 . 031 m) (0 . 031 ) parenleftbigg 1000 mm 1 m parenrightbigg = . 267023 mm . 002 10.0 points A length of copper wire has a resistance 32 . The wire is cut into three pieces of equal length. The pieces are then connected as parallel lengths between points A and B. What resistance will this new wire of length L 3 have between points A and B? Correct answer: 3 . 55556 . Explanation: Let : R = 32 . The new wire has length L = L 3 and cross section A = 3 A , so its resistance is R = L A = parenleftbigg L 3 parenrightbigg 3 A = 1 9 parenleftbigg L A parenrightbigg = R 9 = 32 9 = 3 . 55556 . 003 10.0 points A 11 V battery delivers 116 mA of current when connected to a 74 resistor. Determine the internal resistance of the battery. Correct answer: 20 . 8276 . Explanation: Let : V = 11 V , I = 116 mA = 0 . 116 A , and R = 74 . The internal resistance is in series with the given resistor, so V = I ( R + r ) r = V I R = 11 V . 116 A 74 = 20 . 8276 . 004 10.0 points A platinum resistance thermometer has a re sistance of 200 when placed in a ice 0 C bath and 169 when immersed in a crucible containing a melting substance. What is the melting point of the substance? The temperature coefficient of the platinum hopkins (tlh982) HW 05 criss (4908) 2 is 0 . 00392( C) 1 . Correct answer: 36 . 4408 C. Explanation: Let : T = 20 C , R 1 = 200 , T 1 = 0 C , R = 169 , and = 0 . 00392( C) 1 . The resistance at 20 C is R = R 1 1 + ( T 1 T ) = 200 1 + [0 . 00392( C) 1 ] (0 C 20 C) = 217 . 014 , and R = R [1 + ( T T )] = R + R ( T T ) T T = R R R T = T + R R R T = 20 C + 169  217 . 014 [0 . 00392( C) 1 ](217 . 014 ) = 36 . 4408 C . 005 (part 1 of 4) 10.0 points An energy plant produces an output potential of 4300 kV and serves a city 176 km away. A highvoltage transmission line carries 690 A to the city. The effective resistance of a trans mission line [wire(s)] is 4 . 68 / km times the distance from the plant to the city....
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 Fall '08
 RobertR.Criss
 Physics, Light

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