18-2 - brown(twb493 – Ch18-h2 – chiu –(56565 1 This...

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Unformatted text preview: brown (twb493) – Ch18-h2 – chiu – (56565) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points In a particular wire in a ciruit, conventional current flows in the +y direction. What is the direction of the electron current in the wire? 1. − z 2. − y correct 3. − x 4. + z 5. + x Explanation: Electron current in this case flows in the − y direction. Electron current flows opposite the conventional current. 002 10.0 points Given that the electron current through a wire is 3 . 3 electrons / s, what is the magnitude of the conventional current through it? Use e = 1 . 6 × 10 − 19 C . Correct answer: 5 . 28 × 10 − 19 A. Explanation: I = | q | i ≈ ( 1 . 6 × 10 − 19 C / electrons ) (3 . 3 electrons / s) ≈ 5 . 28 × 10 − 19 A 003 (part 1 of 2) 10.0 points A current-carrying wire oriented north-south and laid over a compass deflects the compass 13 ◦ East. The horizontal component of the Earth’s magnetic field is about 2 × 10 − 5 T . What is the magnitude of the magnetic field made by the current? Correct answer: 4 . 61736 × 10 − 6 T. Explanation: The compass experiences a northward force due to B earth and an Eastward force due to B wire , making it point 13 ◦ east of north. Hence, we can write: | vector B wire | = | vector B Earth | tan θ ≈ ( 2 × 10 − 5 T ) tan13 ◦ ≈ 4 . 61736 × 10 − 6 T . 004 (part 2 of 2) 10.0 points What is the direction of the magnetic field made by the current? 1. West 2. South 3. North 4. East correct Explanation: At a location directly under the current carrying wire, the magnetic field due to the wire is perpendicular to it, and hence should point either east or west. The magnetic field lines due to the wire are determined by the right hand rule. The compass needle points in the direction of the net magnetic field, which is the superposition of the Earth’s magnetic field and that of the current carrying wire....
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This note was uploaded on 12/01/2011 for the course PHY 303L taught by Professor Turner during the Fall '08 term at University of Texas.

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18-2 - brown(twb493 – Ch18-h2 – chiu –(56565 1 This...

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