In the previous activities, you discovered that wires carrying a current can make a compass deflect, and are themselves deflected by a magnet. By making a coil of wire, we can make the effect larger. The resulting device is called an electromagnet.

Assemble these materials:

• 120 cm (4 ft) of copper magnet wire *
• a small piece of sandpaper (to take the insulation off of the ends of the wire) *
• two battery holders and batteries *
• a compass *
• a large nail *
• plastic straw *
• a wire with alligator clip ends *
• some paper clips

In your kit you will find a small coil of copper wire. It looks like bare wire but actually there is a thin coat of transparent paint on it, which serves as insulation. You will need a piece of this wire about 120 cm (4 feet) long.

Use sandpaper to scrape the insulation from the last cm (1/2 inch) of each end of the wire. Be sure to get the wire clean here, or the connections will be bad. Wrap the wire around a plastic straw, always going around in the same way, and keeping the coil gathered in so that it covers only about 1 cm (1/2 inch) of the straw. Leave 12 cm (5 inches) of the wire unwrapped at each end. When you have finished wrapping the coil, cut off the end of the straw so that the coil is 1/2 cm (1/4 inch) from the end.

The following observations require making a complete electrical circut using the coiled wire and a pair of batteries connected in series. Be aware that this circuit rapidly removes energy from the battery, so that you should disconnect the battery when you are not making observations. Record your observations in your journal

• Use your compass to check that there are no magnets or magnetic materials near the coil. Then observe the effect of the coil on the compass, when it is connected to the batteries and when it is not connected to a battery.
• Observe what happens when you reverse the batteries, so that current flows the other way in the coil.
• Make a map of the directions that the compass needle points in regions near the coil, and compare this to the maps you made with magnets.
• Put a large nail inside the coil, and observe how it behaves
  • before you turn on the current,
  • while the current is flowing
  • after you disconnect the batteries
  • when you reverse the current flow by reversing the batteries.
  Is the coil able to pick up a paper clip while it is connected to the batteries (without the nail inside)? How does putting the nail inside the coil affect this?

Check the box when you are done:  
Next:Making a motor