Phys240_2006_E1_solutions

Phys240_2006_E1_solutions - FORM 1 Physics 240 First Exam...

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1 FORM 1 Physics 240 First Exam Fall 2006 1. Please print your name: __________________________________________________ Last First 2. Circle your discussion instructor and section: Instructor Time Section Skalsey 8-9 004 Skalsey 9-10 005 Skalsey 10-11 006 Chapman 9-10 007 Chapman 10-11 008 Chapman 11-12 009 Lubensky 10-11 010 Lubensky 11-12 012 Lubensky 12-1 013 Bobkov 1-2 014 Instructor Time Section Bobkov 2-3 015 Bobkov 3-4 016 Bobkov 5-6 017 Bobkov 6-7 018 Bobkov 7-8 019 Savit 12-1 023 Savit 1-2 024 Savit 2-3 025 Skalsey 5-6 026 3. Fill in your name, student ID number, section number, and the exam version (form) number on the scantron sheets. 4. There are twenty multiple choice questions, worth 5 points each, for a total of 100 points. You must mark the best answer on the scantron sheet to get credit for the problem . There is no penalty for guessing, so be sure to enter an answer for every question. 5. At the end of the exam, hand in your scantron sheet AND your exam copy. 6. The exam is closed book. You may use a calculator and one 3”x5” card of notes. 7. This is a 90 minute exam. k = π ε 0 = 9 × 10 9 N m 2 2 0 = 8.85 × 10 12 C 2 m 2 e = 1.6 × 10 19 C 1 eV = 1.6 × 10 19 J

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2 1. Three identical charges of magnitude Q are placed at the corners of a square of size L . What is the magnitude of the electrical force on the charge located at the lower left corner? (The correct answer is e.) a) Q 2 4 πε 0 L 2 b) 3 Q 2 8 0 L 2 c) Q 2 4 0 L 2 1 + 1 d) Q 2 4 0 L 2 1 + 1 e) Q 2 4 0 L 2 1 + 1 2 + 1 2 2. Which of the following statements about electric field lines is FALSE ? a) Electric field lines cannot cross each other. b) If there is not an electric field line passing through a point P, the electric field must be zero at that point. (The correct answer is b.) c) Electric field lines are used as a representation of the electric field. d) Electric field lines are perpendicular to equipotential surfaces. e) Electric field is larger in a region where the electric field lines are denser. L L Q Q Q
3 3. Consider two electrons far apart, each with a speed of v, traveling towards each other. The closest spacing between the electrons, before they bounce away from each other, is proportional to: (The correct answer is a.) a) 1 v 2 b) 1 c) d) v e) v 2 4) The following diagrams illustrate an electric dipole, represented by the large arrow, in a nonuniform electric field. In which of these configurations is the potential energy of the electric dipole the lowest? The correct answer is a (5 points), partial credit is give for c (2 points).

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Phys240_2006_E1_solutions - FORM 1 Physics 240 First Exam...

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