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Protector: How Can Magnetic Materials Be Shielded From a Magnetic Force Field?

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Author: Janice VanCleave

Problem

How can magnetic materials be shielded from a magnetic force field?

Materials

  • scissors
  • ruler
  • cardboard
  • 2 pencils
  • masking tape
  • bar magnet
  • 10 paper clips
  • stainless steel cake-server

Procedure

  1. Cut two 8-inch × 4-inch (20-cm × 10-cm) cardboard pieces.
  2. Put the pencils between the card-board pieces, as shown in the diagram.
  3. Tape the ends of the cardboard pieces together to secure the cardboard-and-air sandwich.
  4. Tape the magnet near the edge of the top piece of cardboard.
  5. Place all 10 paper clips on a wooden table.
  6. Hold the cardboard sandwich high above the paper clips.
  7. Slowly lower the cardboard sandwich until it is just above, but not touching, the clips.
  8. Observe any movement of the paper clips.
  9. Without moving the cardboard, slowly insert the cake-server between the two pieces of cardboard.
  10. Again, observe any movement of the paper clips.

Protector

Results

The paper clips are first pulled up and cling to the bottom of the cardboard-and-air sandwich. The clips fall when the metal cake-server is inserted between the cardboard pieces.

Why?

The magnetic lines of force from the magnet pass through the cardboard and air, as indicated by the attraction of the paper clips toward the magnet. Materials that allow magnetic lines of force to pass through them are said to be nonpermeable. The stainless steel cake-server acts as a magnetic shield. The force lines coming from the north pole of the magnet do not pass through the cake-server and then continue to move outward. Instead, they are gathered in, travel down the metal server, and re-enter the magnet at its south pole. Materials that gather magnetic lines of force are said to be permeable. Only magnetic materials are permeable.

Let's Explore

  1. What other materials are permeable? Repeat the experiment, but replace the cake-server with other materials such as paper, glass, wood, plastic, rubber, and aluminum foil. Science Fair Hint: Use magazine pictures to make a poster of permeable and nonpermeable items. The poster can be used as part of a project display.
  2. Does the shape of the magnet affect the permeability of materials held near the magnet? Repeat the original experiment using different-shaped magnets. Science Fair Hint: Display drawings or photographs to indicate the results of using different-shaped magnets.

Show Time!

Use iron filings to show the effect of permeable and non permeable materials on magnetic lines of force. Place a horseshoe magnet on a table, with an iron nail near but not touching the poles of the magnet. Cover the magnet with a sheet of paper. Sprinkle iron filings on the part of the paper that is covering the magnet. Repeat the experiment, but replace the nail with a wooden stick. Make drawings and/ or take photographs of the patterns formed by the iron filings. These diagrams and photographs can be displayed to show the effect of permeable materials and nonpermeable materials.

Protector

Check It Out!

Like a bar magnet, the earth has a magnetic field around it. This field, called the magnetosphere, protects the earth from powerful space radiation. Read about this protective shield. You could include this information in an oral report and create a diagram showing the shape of the magnetosphere with its tail-like extension trailing outward toward the sun.

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