# hw12 - homework 12 LEE BENJAMIN Due Oct 2 2007 4:00 am...

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homework 12 – LEE, BENJAMIN – Due: Oct 2 2007, 4:00 am 1 Question 1, chap 27, sect 1. part 1 of 1 10 points How long does it take for 14 C of charge to pass through a cross-sectional area of a copper wire if I = 15 A? Correct answer: 0 . 933333 s (tolerance ± 1 %). Explanation: Let : I = 15 A and Δ Q = 14 C . I = Δ Q Δ t Δ t = Δ Q I = 14 C 15 A = 0 . 933333 s . Question 2, chap 27, sect 2. part 1 of 3 10 points Consider two cylindrical conductors made of the same ohmic material. Conductor 1 has a radius r 1 and length 1 while conductor 2 has a radius r 2 and length 2 . Denote: The currents of the two conductors as I 1 and I 2 , the potential diFerences between the two ends of the conductors as V 1 and V 2 , and the electric ±elds within the conductors as E 1 and E 2 . V 1 v E I r 1 b 2 r 2 b If ρ 2 = ρ 1 , r 2 = 2 r 1 , ℓ 2 = 3 1 and V 2 = V 1 , ±nd the ratio R 2 R 1 of the resistances. 1. R 2 R 1 = 4 2. R 2 R 1 = 2 3. R 2 R 1 = 2 3 4. R 2 R 1 = 1 3 5. R 2 R 1 = 3 2 6. R 2 R 1 = 3 4 correct 7. R 2 R 1 = 4 3 8. R 2 R 1 = 1 4 9. R

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hw12 - homework 12 LEE BENJAMIN Due Oct 2 2007 4:00 am...

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