HANDS-ON SCIENCE ACTIVITY-BUILDING AN ELECTROMAGNET

Materials:

Iron or steel nail, about 1 meter of insulated wire, scissors, battery, paper clips, magnetic compass
 
Instructions:
  • Strip about 2 cm of insulation off the ends of the wire. Wrap the wire tightly around the nail, leaving
    15-20 cm of wire hanging loose at the ends. Connect one end of the wire to one of the battery terminals and tape the lead to the battery. Leave the other end of the wire loose and, when you are ready
    to complete the circuit, you can touch this wire to the other battery terminal. However,
    do this only briefly so that you do not exhaust the battery.
  • With the circuit open, bring the wire-wrapped nail close to the side of the compass, about
    1 cm away, as shown in the diagram. Observe the effect on the compass.
  • Now, close the circuit by touching the loose wire to the second battery terminal.
    Observe the effect on the compass.
  • With the circuit open, turn the nail around with the other end facing the compass.
    Close the circuit and observe the effect on the compass.
  • Bring the coil-wrapped nail near a pile of paper clips and pick up paper clips with the magnet.

Questions for students:
(1) Does the compass needle behave in the same way with either end of the nail near the compass?

(2) Which end of the nail is the north pole of the electromagnet and which end is the south pole?
      How did you decide?

(3) How many paper clips can the magnet pick up?

(4) How can you change the apparatus in order to pick up more paper clips?

(5) When the battery is disconnected after the experiment, does the nail still pick up any paper clips?
      If so, why?

Discussion: This is a classic demonstration of an electromagnet. The activities with the compass demonstrate that the nail is acting as a magnet when the circuit is closed. When the magnet is used to pick up paper clips, make it clear to students that this is a simulation of a large junkyard magnet picking up metal refuse.

More paper clips can be picked up by strengthening the magnetic field. Possible methods for doing this include wrapping more wire around the nail and using a battery with a higher voltage.

If the nail still picks up paper clips after the battery is disconnected, the nail has become weakly magnetized. This can lead to a discussion of permanent magnets.