Wilson/Buffa Section 19.1, 19.7, 19.8, 19.6 (RHR's qualitative only). pg 687 MC #'s 1- 5, 17-20, 21, 24-27, CQ #'s 1-3, 21-24, 26, 28, 30-32 Multiple Choice: 1. (a), because unlike poles attract. 2. (a). 3. (c). 4. (b). A calibrated compass points toward the Earth’s north geographic pole, which is really a south magnetic pole. Therefore it would be attracted by the south pole and repelled by the north pole of the magnets shown, and hence would point downward. 5. (d). 17. (c). By the right hand rule, with the thumb pointing from east to west, the curled fingers point to the south below the wire. 18. (a). By the right hand rule, if the thumb points along the current in a clockwise direction, the curled fingers point away from you. 19. (b), according to the right-hand source rule. 20. (c). The point at the center is closest to the current and hence will have the largest field. The point 20 cm out from the center is farthest and will therefore have the smallest field. 21. (b). 24. (d). 25. (b). 26. (c). The calibrated compass is attracted to the Earth’s north geographic pole and repelled by its south geographic pole. Since the magnetic points straight up, it is being repelled away from the ground, so you must be near the south geographic pole. 27. (a). In order to provide the centripetal force to keep the proton in orbit, the magnetic force must be pointing toward ξ t Concept Questions 1. The magnet would attract the unmagnetized iron bar when a pole end is placed at the center of its long side. If the end of the unmagnetized bar were placed at the center of the long side of the magnet, it would not be attracted. 2. Near the north pole of a permanent bar magnet, the north pole of a compass will point away from the bar magnet so field lines leave a north pole. Near the south pole of a permanent bar magnet, the south pole of a compass will point toward the bar magnet so field lines enter a south pole. 3. (a) The spacing of the iron filings gets farther apart . This tells us that the magnetic field strength decreases with distance from the middle. (b) The magnetic field points up-and-down (parallel to the line along which the magnets are aligned). But we cannot tell if it points up or down from looking at the filing pattern alone. 21. The compass points downward so the magnetic field is downward at the center of the loop. The current direction is clockwise according to the right- hand source rule. 22. Because Bd∝1 you need to double the current and reverse its direction . 23. Not necessarily . The magnetic field in a solenoid depends on the current in it and the number of turns per unit length (the density of turns), not just the number of turns. For example, if the 200 turns is over 0.20 m and the 100 turns is over 0.10 m, then they will have the same turns per unit length and the same magnetic field. 24. There are two wires, one carrying the current into the appliance and the other carrying it out. These two currents are in opposite directions. When the two wires are very close to each other, the magnetic fields created by the two opposite currents essentially cancel. 26. The direction of the magnetic field is away from you , according to the right- hand source rule (remember, the electron has negative charge). 28. You can destroy or reduce the magnetic field of a permanent magnet by hitting or heating it. Also if placed in an external magnetic field its direction can be reversed to match that field’s direction. In a rapidly oscillating external magnetic field, the domains can be left randomized and the bar magnet could have zero residual permanent magnetization. 30. Applying the right-hand rule and recalling that an electron is negative, we get (a) zero (because the velocity is parallel to the magnetic field), (b) upward , and (c) eastward . 31. It will be the north magnetic pole . Right now, the pole near the Earth’s geographical North Pole is actually a south magnetic pole. 32. Using Fig. 19.30, we have: (a) Approximately 12.5∞E since Phoenix is about midway between the 10°E and 15°E isogonic lines. (b) About 2∞W since Chicago is a little less than midway between the 0° and 5°W isogonic lines. 1 (c) About 22 ∞E since New Orleans is about midway between the 0° and 5°W isogonic lines. .