ism_ch22 - Chapter 22 Magnetism Answers to Even-numbered...

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78 Chapter 22 Magnetism Answers to Even-numbered Conceptual Questions 2. Yes. If an electric field exists in this region of space, and no magnetic field is present, the electric field will exert a force on the electron and cause it to accelerate. 4. The magnetic field in the continental United States points primarily toward the north. Therefore, an electron moving toward the east experiences a downward magnetic force. Of course, the magnetic force on a positively-charged proton moving toward the east is upward. 6. In this case, the magnetic force on the electron points to the east. 8. In each case, the force acting on the particle must point toward the center of curvature of its path. Therefore, particles 1 and 2 have negative charges; particle 3 has a positive charge. 10. We want the magnetic force on the proton to be toward the center of the Earth, so that it provides some of the necessary centripetal force. It follows that the proton must move in a westward direction. 12. In a uniform electric field, the force on a charged particle is always in the same direction, leading to parabolic trajectories. In a uniform magnetic field, the force of a charged particle is always at right angles to the motion, resulting in circular or helical trajectories. Perhaps even more important, a charged particle experiences a force due to an electric field whether it is moving or at rest; in a magnetic field, the particle must be moving to experience a force. 14. The electric field must point in the positive x direction, regardless of the sign of the particle’s charge. 16. A current-carrying wire in a uniform magnetic field can experience zero force only if the wire points in the same or opposite direction as the magnetic field. In such a case, the angle θ in Equation 22-4 will be either 0 ˚ or 180 ˚ , in which case F = ILB sin = 0. 18. The force between wires carrying currents in the same direction is attractive, and inversely proportional to the distance between the wires. Similarly, the force between wires with oppositely directed currents is repulsive. It follows from simple geometry, then, that the net force acting on wire 2 is directed toward wire 4. 20. If we apply the right-hand rule to wires 2 and 4, we see that they produce magnetic fields at the center of the square that point toward wire 3. On the other hand, the magnetic fields produced by wires 1 and 3 at the center of the square cancel one another. It follows that the total magnetic field at the center of the square points toward wire 3. 22. If the current loop is to attract the magnet, it must produce a magnetic field with its north pole pointing to the right; that is, pointing toward the south pole of the bar magnet. For this to be the case, the current in the wire must point out of the page, which means, in turn, that terminal A must be the positive terminal.
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Physics: An Introduction Chapter 22: Magnetism Solutions to Problems 1.
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This note was uploaded on 04/08/2008 for the course PHYS 104 taught by Professor Pengyi during the Fall '08 term at UNC.

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ism_ch22 - Chapter 22 Magnetism Answers to Even-numbered...

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