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Unformatted text preview: Create assignment, 00224, Homework 7, Mar 18 at 6:05 pm 1 This printout should have 19 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Charge in a Magnetic Field 04 29:01, trigonometry, multiple choice, > 1 min, fixed. 001 A particle with charge q and mass m is un dergoing circular motion with speed v . At t = 0, the particle is moving along the nega tive x axis in the plane perpendicular to the magnetic field ~ B , which points in the positive z direction in the figure below. x y z ~v ~ B Find the direction of the instantaneous ac celeration b a at t = 0 if q is negative. 1. b a = ˆ i 2. b a = ˆ j correct 3. b a = ˆ i 4. b a = ˆ j 5. b a = ˆ k 6. b a = ˆ k 7. b a = ˆ k + ˆ i 8. b a = ˆ i + ˆ j 9. b a = ˆ k + ˆ i 10. b a = ˆ j + ˆ k Explanation: The particle is moving along the negative xaxis in this instant ~v = v ˆ i ; since it is moving in a circle, we need to talk about instantaneous direction. The force F B is equal to q ~v × ~ B at all times. We know that ~ B is pointing in the z direction, so ~ B = B ˆ k , and therefore ~ F B = q v ( ˆ i ) × B ˆ k = q v B ( ˆ i × ˆ k ) = q v B ˆ j . The charge q is negative ( q = q  ) , so ~ F B = q  v B ˆ j =  q  v B ( ˆ j ) . All quantities are positive, so the actual di rection in which ~ F B points is the negative y direction, or b a = ˆ j . keywords: Conceptual 17 02 29:01, highSchool, numeric, > 1 min, normal. 002 The strength of Earth’s magnetic field B at the equator is approximately equal to 5 × 10 5 T, where T stands for tesla, the unit of magnetic field. The force on a charge q moving in a direction perpendicular to a mag netic field is given by F = q v B , where v is the speed of the particle. The direction of the force is given by the righthand rule. Suppose you rub a balloon in your hair and your head acquires a static charge of 3 × 10 9 C. If you are at the equator and driving west at a speed of 30 m / s, what is the strength of the magnetic force on your head due to Earth’s magnetic field? Correct answer: 4 . 5 × 10 12 N. Explanation: Let : q = 3 × 10 9 C , v = 30 m / s , and B = 5 × 10 5 T . Create assignment, 00224, Homework 7, Mar 18 at 6:05 pm 2 F = q v B = (3 × 10 9 C) (30 m / s) (5 × 10 5 T) = 4 . 5 × 10 12 N . 003 What is the direction of that magnetic force? 1. east 2. west 3. north 4. south 5. upward correct 6. downward Explanation: The direction of the magnetic force is up ward by the righthand rule. 004 If you are at the equator and driving north at a speed of 30 m / s, what is direction of the magnetic force on your head?...
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This note was uploaded on 04/08/2011 for the course PHYS 1402 taught by Professor Avram during the Spring '10 term at Austin Community College.
 Spring '10
 Avram
 Physics, Charge, Work

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