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Temporary: How Can You Make a Magnet by Induction?

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Author: Janice VanCleave

Problem

How can you make a magnet by induction (magnetism produced when a magnetic material enters the field of a magnet)?

Materials

  • cardboard, about 1 foot (30 cm) square
  • thin book
  • index card
  • masking tape
  • bar magnet
  • box of BBs

Procedure

  1. Place the edge of the cardboard on top of the book to form an incline.
  2. Bend up about 1 inch (2.5 cm) of one short end of the index card.
  3. Tape the card to the cardboard with the bent edge up and facing the book (see diagram).
  4. Place the magnet on the cardboard, with the north pole facing the card. Move the magnet as close as possible without actually touching the index card.
  5. Hold a BB against the upturned side of the index card. It should remain in position when released.
  6. Touch the first BB with a second BB.
  7. Continue adding BBs to the chain until the BBs no longer cling together.
  8. Slowly move the magnet away from the chain of BBs.

Temporary

Results

The number of BBs that cling together and hang down the incline will depend on the strength of the magnet. As soon as the magnet is moved away, the BBs pull away from each other and roll down the incline.

Why?

Every magnet is surrounded by a magnetic force field. The steel BBs, or any other magnetic materials, become magnets when placed in a magnetic field. Atoms act like tiny magnets with both a north and a south pole. When the magnetic material is placed near a magnet, the atoms in the magnetic material are pulled on by the magnet's force field, causing them to turn so that many of them point uniformly in the same direction.

The atoms in the first BB do not actually touch the magnet, but the magnetic force from the bar magnet enters the BB, causing the atoms to line up in the same direction as those in the magnet. The second and following BBs become magnetized in a similar way, but the force field comes from the magnetized BB it touches. Magnetism created in a magnetic material by touching or being near a magnet is called induced magnetism. The magnetic strength of the BBs depends on the strength of the magnetic field around the magnet and how close it is to the BBs. The force field from the bar magnet becomes weaker as the distance from the magnet increases. As the force field weakens, fewer atoms in the BBs line up. As a result, the BBs lose their magnetic power, pull away from each other, and roll down the incline.

Let's Explore

  1. Would holding a different part of the magnet near the BBs affect the results? Repeat the experiment by first reversing the ends of the magnet, and then turning the magnet so that the side of the magnet is facing the index card. Science Fair Hint: Display diagrams showing the results of holding different parts of the magnet near the BBs.
  2. Will other magnetic materials become temporarily magnetized by induction in the presence of a strong magnet? Repeat the original experiment using magnetic materials such as steel paper clips, thumbtacks, or pins. Science Fair Hint: Photographs and/or diagrams can be used to demonstrate temporary magnets (magnets that exhibit magnetic power only when touching, or placed near, a magnet) made from different materials.
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