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Line Up: How Can You “See” a Magnetic Field?

based on 3 ratings
Author: Janice VanCleave

Problem

How can you "see" a magnetic field?

Materials

  • 2 bar magnets
  • 2 sheets of paper
  • large paper cup
  • iron filings (found in magnetic drawing toys sold at toy stores)

Procedure

  1. Arrange the 2 magnets end to end on a wooden table, with their north poles about 2 inches (5 cm) apart.
  2. Cover the magnets with the first sheet of paper.
  3. Fill the paper cup with the iron filings. Slowly sprinkle some of the filings over the part of the paper that is covering the magnets.
  4. Observe the pattern formed by the iron filings on the paper.
  5. After removing the first sheet of paper, rearrange the magnets so that the north pole of the first magnet is about 2 inches (5 cm) away from the south pole of the second magnet
  6. Cover the magnets with the second sheet of paper. Sprinkle the remaining iron filings over the part of the paper that is covering the magnets.
  7. Observe the pattern formed by the iron filings on the paper.

Line Up

Results

The iron filings form curved lines around each magnet, regardless of how the magnets are arranged. The pattern of the filings changes near the magnet poles (ends) that have been placed near another magnet. The lines formed by the filings bend away from each other at the ends where the north poles face each other. When north and south poles face each other, lines of iron filings curve from the end of the first magnet toward the end of the second magnet.

Why?

Every magnet has an invisible magnetic field around it. This field is made up of lines of force that attract magnetic material such as iron filings. The filings form a pattern as they line up in the direction of the magnetic lines of force. The lines of force around each magnet come out of the north pole, loop around the magnet, and enter the magnet's south pole. The magnetic forces of two "like" poles, such as two north poles, repel each other. Placing two north poles near each other results in the iron filings at the facing ends being pushed away from the neighboring magnet. "Unlike" poles of magnets attract each other. Placing north and south poles of magnets near each other results in a magnetic field that comes out of the north end of the first magnet and moves toward the facing south pole of the second magnet. The iron filings line up with their force field forming a bridge of filings between the two magnets.

Line Up

Let's Explore

  1. Would placing the south poles of the magnets near each other produce a different pattern? Repeat the experiment, placing the magnets so that their south poles face each other.
  2. Would laying the magnets side by side change the pattern of the iron filings?
  3. Repeat the original experiment, placing the magnets so that they are lined up side by side.

  4. Does the shape of the magnet affect the pattern of the iron filings? Repeat the original experiment using different-shaped magnets. Science Fair Hint: Photographs and drawings showing the iron filing patterns around the magnets can be used as part of a project display.

Show Time!

On a piece of cardboard, position different-shaped magnets. In one area, position the magnets with "like" poles facing each other, and in a second area, have the "unlike" poles of the magnets facing each other. Cover the magnets with a large sheet of white paper. Sprinkle iron filings over the surface of the paper. Gently tap the paper with your finger and the filings will form a pattern of the force field around the magnets. Use a spray bottle to cover the paper with a fine mist of white vinegar. Allow the paper to remain undisturbed for several hours—enough time for the iron filings to rust. Later, turn the paper over and brush off the rusty filings. The rust marks will remain on the paper to record the shapes of the magnetic fields around each magnet.

Line Up

Check It Out!

Read about Michael Faraday. This 19th-century English scientist was the first person to make it possible to visualize magnetic lines of force around a magnet. Find out how this self-taught genius with no math or science training became someone whose advice was sought by important scientists of his day. Include this information in your project.

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