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Unformatted text preview: Chapter 19 Magnetism Quick Quizzes 1. (b). The force that a magnetic field exerts on a charged particle moving through it is given by sin F qvB qvB = = , where B is the component of the field perpendicular to the particles velocity. Since the particle moves in a straight line, the magnetic force (and hence B , since qv ) must be zero. 2. (c). The magnetic force exerted by a magnetic field on a charge is proportional to the charges velocity relative to the field. If the charge is stationary, as in this situation, there is no magnetic force. 3. (c). The torque that a planar current loop will experience when it is in a magnetic field is given by sin BIA = . Note that this torque depends on the strength of the field, the current in the coil, the area enclosed by the coil, and the orientation of the plane of the coil relative to the direction of the field. However, it does not depend on the shape of the loop. 4. (a). The magnetic force acting on the particle is always perpendicular to the velocity of the particle, and hence to the displacement the particle is undergoing. Under these conditions, the force does no work on the particle and the particles kinetic energy remains constant. 5. (b). The two forces are an action-reaction pair. They act on different wires and have equal magnitudes but opposite directions. 141 142 CHAPTER 19 Answers to Even Numbered Conceptual Questions 2. No. The force that a constant magnetic field exerts on a charged particle is dependent on the velocity of that particle. If the particle has zero velocity, it will experience no magnetic force and cannot be set in motion by a constant magnetic field. 4. The force exerted on a current-carrying conductor by a magnetic field is sin F BI = l , where is the angle between the direction of the current and the direction of the magnetic field. Thus, if the current is in a direction parallel ( 29 = or anti-parallel ( 29 180 = to the magnetic field, there is no magnetic force exerted on the conductor. 6. Straight down toward the surface of Earth. 8. The magnet causes domain alignment in the iron such that the iron becomes magnetic and is attracted to the original magnet. Now that the iron is magnetic, it can produce an identical effect in another piece of iron. 10. The magnet produces domain alignment in the nail such that the nail is attracted to the magnet. Regardless of which pole is used, the alignment in the nail is such that it is attracted to the magnet. 12. The magnetic field inside a long solenoid is given by B nI NI = = l . (a) If the length l of the solenoid is doubled, the field is cut in half. (b) If the number of turns, N , on the solenoid is doubled, the magnetic field is doubled....
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