Multiple-Choice Homework Problem 12.1 A strand of the transatlantic cable was 2.

Question

Multiple-Choice Homework Problem 12.1 A strand of the transatlantic cable was 2.54cm in DIAMETER and 4.32 × 106m long. Assume the cable was copper with resistivity 1.7 × 108m. Calculate its resistance. Select One of the Following: (a) 580 (b) 36 (c) 0.0060 (d) 58 (e) 140

Multiple-Choice Homework Problem 12.2 A certain direct current circuit carries a current of 0.50A flowing through a wire. We will assume that the charged particles that move in the wire are electrons. How many electrons flow through a cross-section of the wire in 1.0 minute? Select One of the Following: (a) 1.9 × 1020electrons. (b) 4.8 × 1021electrons. (c) 7.7 × 1016electrons. (d) 3.1 × 1018electrons. (e) 1.2 × 1010electrons.

Explanation / Answer

Resistance = resistivity x length / cross section area

R = (1.7 x 10^-8 x 4.32 x 10^6) / (pi x (0.0254/2)^2)

R = 145 ohm

Ans(e)

................................

I = q/t

q = 0.50 A x (1 x 60s) = 30 C

and q = ne

30 = n (1.6 x 10^-19)

n = 1.87 x 10^20 electrons

Ans(a)

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