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Unformatted text preview: fullwood (tf5349) Homework 3 DC Circuits Catala (12054) 1 This printout should have 24 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points An Xray tube used for cancer therapy oper ates at 4.2 MV with a beam current of 85 mA striking a metal target. Calculate the power of this beam. Correct answer: 3 . 57 10 5 W. Explanation: Let : V = 4 . 2 MV and I = 85 mA . P = I V = (0 . 085 A) (4 . 2 10 6 V) = 3 . 57 10 5 W . 002 10.0 points A wire is made of a material with a resistiv ity of 8 . 05638 10 8 m. It has length 4 . 39265 m and diameter 0 . 50739 mm. What is the resistance of the wire? Correct answer: 1 . 75022 . Explanation: Let : = 8 . 05638 10 8 m , = 4 . 39265 m , and r = 0 . 253695 mm = 0 . 000253695 m . By definition, the resistance of the wire is R = A = r 2 = ( 8 . 05638 10 8 m ) (4 . 39265 m) (0 . 000253695 m) 2 = 1 . 75022 . 003 (part 1 of 3) 10.0 points A total charge of 9.8 mC passes through a crosssectional area of a nichrome wire in 3 . 3 s. a) What is the current in the wire? Correct answer: 0 . 0029697 A. Explanation: Let : Q 1 = 9 . 8 mC and t 1 = 3 . 3 s . I = Q t = . 0098 C 3 . 3 s = . 0029697 A . 004 (part 2 of 3) 10.0 points b) How many electrons pass through the crosssectional area in 49.0 s? Correct answer: 9 . 0947 10 17 . Explanation: Let : q e = 1 . 6 10 19 C and t 2 = 49 . 0 s . Q = N q e N = Q q e = I t 2 q e = (0 . 0029697 A)(49 s) 1 . 6 10 19 C = 9 . 0947 10 17 . 005 (part 3 of 3) 10.0 points c) If the number of charges that pass through the crosssectional area during the given time interval doubles, what is the resulting cur rent? Correct answer: 0 . 00593939 A. Explanation: Let : Q 2 = 2 Q 1 . fullwood (tf5349) Homework 3 DC Circuits Catala (12054) 2 I = 2 Q 1 t 1 = 2 (0 . 0098 C) 3 . 3 s = . 00593939 A ....
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