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Unformatted text preview: Create assignment, 00224, Homework 7, Mar 06 at 6:45 pm 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. Charged Particle in a Field 02 29:01, trigonometry, multiple choice, > 1 min, fixed. 001 A charged particle is projected with its initial velocity parallel to a uniform magnetic field. What is the resulting path? 1. straight line parallel to the field. correct 2. parabolic arc. 3. circular arc. 4. straight line perpendicular to the field. 5. spiral. Explanation: The force on a moving charge due to a magnetic field is given by ~ F = q~v ~ B . If ~v and ~ B are parallel, then ~v ~ B = 0 . Hence the force on the particle is zero, and the particle continues to move in a straight line parallel to the field. keywords: Field Direction 29:01, highSchool, multiple choice, < 1 min, fixed. 002 The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is 1. one of the direction of the velocity when the magnetic field is zero. 2. the direction of the velocity when the magnetic force is a maximum. 3. the direction of the magnetic force. 4. perpendicular to the velocity when the magnetic force is zero. 5. None of these correct Explanation: The magnetic field direction can be deter- mined according to the path of a charge which moves in the field. Since ~ F = q~v ~ B , the component of velocity along the magnetic field doesnt contribute to the magnetic force; i.e., a charge moving along the magnetic field will keep its motion status. On the contrary, if the initial velocity in perpendicular to the magnetic force, there will be a centripetal force so that the charge will undergo circular motion. keywords: Force on an Electron 29:01, trigonometry, numeric, > 1 min, wording-variable. 003 An electron is projected into a uniform mag- netic field given by ~ B = B z k + B x , where B z = 3 . 7 T and B x = 1 . 4 T. The magnitude of the charge on an electron is 1 . 60218 10- 19 C . z x y v = 370000 m / s electron 3 . 7 T 1 . 4 T B Create assignment, 00224, Homework 7, Mar 06 at 6:45 pm 2 Find the direction of the magnetic force when the velocity of the electron is v , where v = 370000 m / s. 1. b F = correct 2. b F =- 3. b F = 4. b F = k 5. b F =- 6. b F =- k 7. b F = 1 2 k + 8. b F = 1 2 k- 9. b F = 1 2 - k Explanation: Let : q = 1 . 60218 10- 19 C , B z = 3 . 7 T , and B x = 1 . 4 T . Basic Concepts: Magnetic force on a mov- ing charge is given by ~ F = q~v ~ B ....
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