Chapter 18 review


    Conceptual questions
      Section 18.1
      1. Identify five different kinds of objects in your home that use magnets.
      2. Is a refrigerator door a permanent magnet?
      3. Does a compass needle show the magnitude or direction of the Earth’s magnetic field?
      4. Easy Describe a procedure to use a magnetic compass to find the magnetic north pole of a bar magnet.
      5. Easy A sheet of paper is held in place by two bar magnets on either side of it. Is the paper now magnetized? Why or why not?
      6. Easy The north magnetic pole of a bar magnet is observed to demagnetize a credit card’s magnetic stripe. Will the south magnetic pole of the same bar magnet also demagnetize the stripe?
      7. Easy Describe how a compass can be used to trace out the magnetic field around a bar magnet.
      8. Easy Will a compass needle point in the same or opposite direction as a magnetic field line?
      9. Easy One end of a bar magnet is labeled with a red “N” for north magnetic pole, but the other end is not labeled. Is the unlabeled end of the magnet a north magnetic pole, a south magnetic pole, or neither?
      10. Easy Sketch the magnetic field lines around a bar magnet.
      11. Easy Is Earth’s magnetic north pole located near Earth’s geographic north pole? Why or why not?
      12. Easy Why don’t most magnets align themselves with the Earth’s magnetic field?
      13. Easy When you want to trace out the magnetic field of a bar magnet, why do you place a piece of paper or poster board on top of a bar magnet before pouring iron filings out of a container onto it?
      14. Easy As a compass moves around a bar magnet, the compass needle is repeatedly caused to move. What is the source of the needle’s kinetic energy?
      15. Medium Cynthia is standing at the location that corresponds to Earth’s north magnetic pole. What direction will her compass point? How about if she were standing at Earth’s south magnetic pole?
      16. Medium Why don’t compasses work when they are held upside-down or sideways?
      1. Medium A physics teacher opened a box of bar magnets and found that none of them had north and south ends labeled. How could he figure out their magnetic poles? What other equipment would he need?
      2. Medium Explain the differences between how you would find the direction of geographic north if you had a compass but were located in (a) California, (b) Missouri, or (c) Maine.
      3. Medium When you use iron filings to trace out the magnetic field around a bar magnet, how can you distinguish the magnet’s north and south magnetic poles from each other?
      4. Medium Two bar magnets are connected together, end to end, with the north end of one connected to the south end of the other. Sketch the magnetic field lines around this composite bar magnet.
      5. Medium Imagine two identical bar magnets placed side by side, with their poles aligned in the same direction. Does the magnetic force cause a torque on either bar magnet? How about if their poles were aligned in opposite directions?
      6. Medium Imagine two identical bar magnets placed next to each other such that the north magnetic pole of one is near the middle of the other bar magnet. Does the magnetic force cause a torque on either bar magnet?
      7. Medium What is the evidence that Earth’s magnetic field can be represented by a large bar magnet?
      8. Medium Which has more energy available, the magnetic field created when the north poles of two bar magnets are moved to a separation of 1 cm or 10 cm?
      9. Challenging What might cause the Earth’s magnetic field to change over time?
      Section 18.2
      1. Why does the gravitational force between the Sun and Earth dominate over the electrical force?
      2. Do negatively charged particles attract or repel each other? What about positively charged particles?
      3. Why don’t the electrical charges in your body attract those in the wall?
      4. Why is it a bad idea to discharge static electricity on the circuit board inside a computer?
      5. Provide three examples of electric force in everyday life.
      6. Easy Why does a comb sometimes attract your hair toward it?
      7. Why do you sometimes get shocked when you touch a doorknob on a dry day?

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