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Attractive Spirals: What is an Electromagnet?

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Author: Janice VanCleave

Problem

What is an electromagnet?

Materials

  • box of BBs
  • saucer
  • 2 inch × 3 feet (5 cm ×1 cm) strip of aluminum foil
  • 1 new, clean penny
  • short, wide rubber band
  • long iron nail
  • D-cell battery

Procedure

  1. Place 5 or 6 BBs in the saucer.
  2. Fold the foil strip in half lengthwise three times to form a thin strip that acts like and will be called a wire.
  3. Wrap the foil tightly around the nail. Neatly overlap the layers leaving about 6 inches (15 cm) of free wire on each end.
  4. Wrap one end of the foil wire around the penny. Tape the wrapped coin to the negative battery terminal and the second foil end to the positive terminal. Stretch the rubber band around the battery to hold the ends.
  5. Holding the battery, touch the point of the nail to a BB in the saucer.
  6. Lift the nail.
  7. Keep the ends of the wire on the battery poles, and try to pick up a chain of BBs on the end of the nail. WARNING: In 10 seconds, or when the battery begins to feel warm, remove the ends from the battery poles.
  8. Attractive Spirals

Results

A small chain of metal BBs clings to the end of the nail.

Why?

Electric currents can be used to produce a magnet. A magnetic field circles any wire carrying an electric current. Winding the foil into a coil (like a spring) pushes the magnetic field closer together and increases the strength of the magnet formed by the flowing electricity. Any coiled wire through which electricity flows is called a solenoid. The electric current flowing through the coils turns the wire into a magnet. Wrapping the foil around an iron nail produces a stronger magnet because the magnetism from the coils magnetizes the nail. The strength of the magnetism from the solenoid (coiled wire) and of the nail combine to produce a much stronger magnet. Magnets made by an electric current flowing through a wire are called electromagnets.

Attractive Spirals

Let's Explore

  1. Does the number of coils around the nail affect the strength of the electromagnet? Repeat the experiment twice, first by wrapping a longer length of foil around the nail, and then by replacing the long foil with a shorter length of foil. Science Fair Hint: Display the solenoids made with varying lengths of foil as part of a project display. Include a short summary of the magnetic results of each test.
  2. Does the size of the nail affect the strength of the electromagnet? Repeat the original experiment, first replacing the nail with a larger iron nail, and then using a smaller nail inside the solenoid. Science Fair Hint: Display photographs of the different-sized nails used inside the solenoid, showing the chain of BBs that each nail lifted.
  3. How does the amount of electric current affect the strength of an electromagnet? Repeat the original experiment, but this time increase the electric current flowing through the solenoid by replacing the D-cell battery with two D-batteries. Tape the batteries together with the positive and negative ends touching. Attach the ends of the solenoid wire to the poles of the battery and hold the nail in your hand. WARNING: Be sure to disconnect the wire from the battery when the nail begins to feel warm. It could get hot enough to burn your skin, and it drains the charge from the battery. Science Fair Hint: Photographs and or drawings of the two electromagnets produced with D-cell and C-cell batteries can be displayed showing the number of BBs they can lift.

Show Time!

Do the positive and negative ends of the battery affect the north and south magnetic poles on the electromagnet? Prepare an electromagnet as in the original experiment Connect the foil to a battery, and hold the pointed end of the nail near a compass. NOTE: Do not touch the nail to the compass, as it can change the polarity of the compass needle. Reverse the solenoid so that the wire ends touch a different pole, and hold the point of the nail near the compass again. The pointed end of the magnetized nail is a south pole when it attracts the north end of the compass needle, but it is a north pole if it attracts the south end of the compass needle. Make drawings showing the connections of the solenoid wires and the magnetic poles produced as part of a project display.

Attractive Spirals

Check It Out!

Huge electromagnets are used to pick up and transport cars at scrap yards. Read about electromagnets and find out about other uses for electromagnets. Select colorful magazine pictures of instruments containing electromagnets. Prepare a poster with these pictures that can be used as part of a project display.

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