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Unformatted text preview: Anderson, Matthew – Homework 7 – Due: Mar 11 2008, noon – Inst: Vitaly 1 This printout should have 12 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 2) 10 points The potential difference in a simple circuit is 2 V and the resistance is 3 Ω. What current I flows in the circuit? Correct answer: 0 . 666667 A. Explanation: Let : V = 2 V and R = 3 Ω . The current is I = V R = 2 V 3 Ω = . 666667 A . 002 (part 2 of 2) 10 points How many electrons pass a given point in the circuit in 8 min? Correct answer: 2 × 10 21 . Explanation: Let : I = 0 . 666667 A , t = 8 min = 480 s , and q e = 1 . 6 × 10 19 C . I = q t , where q isincoulombsand t inseconds; that is, q = I t, and the total charge for n electrons is q = n q e , so n = q q e = I t q e = (0 . 666667 A)(480 s) 1 . 6 × 10 19 C = 2 × 10 21 . keywords: 003 (part 1 of 1) 10 points Birds resting on highvoltage power lines are a common sight. The copper wire on which a bird stands is 1 . 75 cm in diameter and carries a current of 5 A. Copper’s resistivity is 1 . 68 × 10 8 Ωm . If the bird’s feet are 1 . 25 cm apart, what is the potential difference across its body? Correct answer: 4 . 36539 μ V. Explanation: Let : r = 0 . 875 cm = 0 . 00875 m , I = 5 A , L = 1 . 25 cm = 0 . 0125 m , and ρ = 1 . 68 × 10 8 Ωm . The resistance of the wire between the feet is R = ρ L A so the potential is Δ V = I R = I ρ L A = (5 A)(1 . 68 × 10 8 Ωm)(0 . 0125 m) π (0 . 00875 m) 2 × 10 6 μ V V = 4 . 36539 μ V ....
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This note was uploaded on 03/11/2010 for the course PHYS 121 taught by Professor Opyrchal during the Spring '08 term at NJIT.
 Spring '08
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