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Integrated Coordinated Science for the 21st Century

Active Physics
+ Chapter 5
Long-Distance Communication
Answers
Physics To Go
  1. a) If no magnet is nearby, the needle points north.
    b) The direction of the needle changed.
    c) That direction is perpendicular to the wire.
    d) If the magnetism of the wire turned the compass to point north, there would be no way to observe that, since the compass is already pointing north.
    e) Adding several batteries end-to-end would increase the effect on the compass.
  2. a) See the drawing on page 265.
    b) The compass points perpendicular to the wire. Note: When the wire carries a current, there are two magnetic fields acting on the compass: the field of the Earth and the field of the wire. The compass lines up along the vector sum of these two fields. Consequently, the compass may wind up pointing between its original direction and the perpendicular to the wire.
    c) The compass reverses direction compared to Part (b).
  3. a) The current produced would have been much weaker.
    b) The compass would have turned more rapidly and probably through a much larger angle. The final direction of the compass would have been perpendicular to the coil.
  4. When the current flowed in the electromagnet, it would have turned the compass to a different direction.
  5. a) In this activity the variables are the number of turns and the number of batteries in series. Another variable is the kind of metal in the nail.
    b) number of turns: as in the activity; size of current: as in the activity, but measure the size of the current each time kind of metal: find several different kinds of nails (brass, steel, zinc, etc.); keep the number of turns and the current the same; measure the number of nails each electromagnet can pick up.
  6. You moved the coil of wire relative to magnet; the coil increased the current produced; you made an electromagnet; the more turns, the stronger the electromagnet.
  7. a - b) Answers will vary.
  8. a - b) Answers will vary.
    c) You will find the electricity used in units of kilowatt-hours. Note the units:
    power X time = energy. Breakers trip or fuses blow when the current becomes too great (to prevent a fire, e.g.).