Section 1 review
Magnets are found in many objects we use every day, such as motors. Permanent magnets maintain their magnetic activity even when not in the presence of other magnets. Some magnetic materials can be temporarily magnetized by the presence of an external magnet. Magnets always have two different magnetic poles, which we call north and south. The force between magnetic poles is attractive between unlike poles and repulsive between like poles. The magnetic force becomes very strong as magnets are brought close together. Magnetic field lines are a tool for visualizing how magnetic fields vary in the space around a magnet. The planet Earth has a magnetic field. The south magnetic pole of Earth’s magnetic field is close to, but not exactly aligned with, the planet’s north geographic pole. The difference between geographic and magnetic north is called declination. Electricity and magnetism are connected with each other because electric current creates a magnetic field. Read the text aloud
magnetic, magnetism, permanent magnet, magnetize, magnetic force, magnetic poles, polarity, force field, magnetic field, magnetic field lines, ferromagnetic, magnetic domains

Review problems and questions

  1. A teacher needs to store two strong permanent magnets in a box. The problem is that they attract each other, stick together, and are very hard to separate. Describe a way to store the two magnets in the same box so that they can be easily separated. Read the text aloud Show
  1. The north magnetic pole of a bar magnet is brought near the middle of a second bar magnet, i.e., halfway between its north and south magnetic poles. The second magnet is observed to spin by 90°. In what direction does it spin? Why? Draw a diagram to illustrate your answer. Read the text aloud Show
  1. What is the cause of Earth’s magnetic field? Read the text aloud Show
  1. Describe the outcome of an experiment in which a student tries to create an isolated north magnetic pole by breaking off the north pole of a permanent magnet. Read the text aloud Show
  1. Which pole of a bar magnet will attract a paper clip? Why? Read the text aloud Show
  1. A typical bar magnet is placed on a table, approximately 10 cm away from a pile of iron filings.
    1. Does the bar magnet or the Earth produce a greater contribution to the magnetic field in the vicinity of the iron filings?
    2. How can you test your answer? Read the text aloud Show
  1. Which of these actions would be more likely to weaken the magnetic field of a bar magnet: placing it in a warm oven or placing it in the freezer? Why? Read the text aloud Show
  1. We know that like magnetic poles repel each other. Yet the north pole of a compass needle points roughly toward the Earth’s North Pole. Why? Read the text aloud Show
  1. How can you use a compass to determine direction? Read the text aloud Show

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