10- Current and current density-solutions

10- Current and current density-solutions - gilvin(jg47854...

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Unformatted text preview: gilvin (jg47854) – 10: Current and current density – meyers – (21235) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This homework is due Tuesday, March 12, at midnight Tucson time. 001 10.0 points A total charge of 4 . 43 mC passes through a cross-sectional area of a wire in 0 . 882 s. What is the current in the wire? Correct answer: 5 . 02268 mA. Explanation: Let : Δ Q = 4 . 43 mC and Δ t = 0 . 882 s . I = Δ Q Δ t = 4 . 43 mC . 882 s = 5 . 02268 mA . 002 10.0 points The drift velocity of free electrons in a cop- per wire is 7 mm / s, resistivity is 1 . 63 × 10- 8 Ω · m, and the free electron density is 8 . 44 × 10 28 electrons / m 3 . Calculate the electric field in the conductor. Correct answer: 1 . 54273 N / C. Explanation: Let : v d = 7 mm / s = 0 . 007 m / s , n = 8 . 44 × 10 28 electrons / m 3 , ρ = 1 . 63 × 10- 8 Ω · m , and q e = 1 . 602 × 10- 19 C / electron . From Ohm’s law, J = σ E = E ρ = n q V d E = n q v d ρ = (8 . 44 × 10 28 electrons / m 3 ) · (1 . 602 × 10- 19 C / electron) · (0 . 007 m / s) (1 . 63 × 10- 8 Ω · m) = 1 . 54273 N / C . 003 10.0 points Calculate the average drift speed of electrons traveling through a copper wire with a cross- sectional area of 40 mm 2 when carrying a current of 50 A (values similar to those for the electric wire to your study lamp). Assume one electron per atom of copper contributes to the current. The atomic mass of copper is 63 . 5 g / mol and its density is 8 . 93 g / cm 3 . Avogadro’s number N A is 6 . 02 × 10 23 ....
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This note was uploaded on 04/29/2011 for the course PHYS 202 taught by Professor Doc during the Spring '11 term at North Texas.

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10- Current and current density-solutions - gilvin(jg47854...

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