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Unformatted text preview: hussain (wh4892) – hw 3 – Opyrchal – (121104) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An electric field of magnitude 28000 N / C and directed upward perpendicular to the Earth’s surface exists on a day when a thunderstorm is brewing. A truck that can be approximated as a rectangle 5 . 4 m by 4 . 4 m is traveling along a road that is inclined 15 ◦ relative to the ground. Determine the electric flux through the bot tom of the truck. Correct answer: 6 . 42611 × 10 5 N · m 2 / C. Explanation: Let : E = 28000 N / C , ℓ = 5 . 4 m , w = 4 . 4 m , and θ = 15 ◦ . By Gauss’ law, Φ = vector E · vector A The flux through the bottom of the car is Φ = E A cos θ = E ℓ w cos θ = (28000 N / C) (5 . 4 m) × (4 . 4 m) cos(15 ◦ ) = 6 . 42611 × 10 5 N · m 2 / C . 002 10.0 points A nonconducting wall carries a uniform charge density of 3 . 75 μ C / cm 2 . What is the electric field 3 . 5 cm in front of the wall? Correct answer: 2 . 11764 × 10 9 N / C. Explanation: Let : σ = 3 . 75 μ C / cm 2 and r = 3 . 5 cm . The electric field of an infinite plane of surface charge density σ is E = σ 2 ǫ = 3 . 75 μ C / cm 2 2 (8 . 85419 × 10 − 12 C 2 / N · m 2 ) × parenleftbigg 1 C 10 6 μ C parenrightbigg · parenleftbigg 100 cm 1 m parenrightbigg 2 = 2 . 11764 × 10 9 N / C . 003 (part 1 of 2) 10.0 points A thin spherical shell of radius 5 . 14 m has a total charge of 4 . 32 C distributed uniformly over its surface. Let : k e = 8 . 988 × 10 9 N · m 2 / C 2 . 5 . 1 4 m vector E + + + + + + + + + + + + + + + + + + + + Find the electric field vector E 10 . 7 m from the center of the shell (outside the shell). Correct answer: 3 . 3914 × 10 8 N / C. Explanation: Let : a = 5 . 14 m , Q = 4 . 32 C , and r = 10 . 7 m . If we construct a spherical Gaussian surface of radius r > a , concentric with the shell, then the charge inside this surface is Q . Therefore the field at a point outside the shell is equiva lent to that of a point charge Q at the center....
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 Spring '08
 moro
 Electrostatics, Correct Answer, Electric charge

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