quiz3_sol

# quiz3_sol - Physics 2B Quiz 3 Summer Session I 2009 Version...

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Unformatted text preview: Physics 2B Quiz 3 Summer Session I 2009 Version 0 Name: PID: Quiz ID: READ FIRST: Make sure to write/fill in your scantron form your name, quiz ID and the test version. e ≈ 1 . 6 × 10- 19 C , k ≈ 9 . × 10 9 N m 2 / C 2 , ≈ 8 . 9 × 10- 12 C 2 / N m 2 , Unless otherwise specified, assume potential is zero at infinity. 1. A wire has a cross-sectional area of 0.1 mm 2 . If there are 5 . × 10 28 atoms per cubic meter and each contributes, on average, 2 free electrons, what is the drift speed of the electrons when the current in the wire is 4.0 A? Solution: The current density is simply the current per area. So J = I/A = 4 . 0 A / . 1 mm 2 = 4 . × 10 7 A/m 2 . The drift speed is related to the current density by: v d = J ne = 4 . × 10 7 A/m 2 2 · 5 . × 10 28 m- 3 · 1 . 6 × 10- 19 C = 0 . 0025m/s A. 2.5 mm/s B. 5.0 mm/s C. 7.5 mm/s D. 1.0 mm/s 2. Mercury has resistivity 9 . 84 × 10- 7 Ω · m. A tube of mercury has a 35.0-V/m electric field inside. How much current is flowing, if the diameter of the tube is 2.0 mm? Solution: Relating conductivity to resistivity, the current density is: J = σE = E ρ = 35 . 0 V/m 9 . 84 × 10- 7 Ω · m ≈ 3 . 56...
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quiz3_sol - Physics 2B Quiz 3 Summer Session I 2009 Version...

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