Investigation 19A: Build an electromagnet

Essential questionsHow are electricity and magnetism connected to each other?
How can you predict the polarity of an electromagnet?
An electromagnet uses electric current to create a magnetic field. An electromagnet is used in an electric motor to attract and repel magnets on a spinning disk. By switching the direction of the electric current, the magnetic field also changes its polarity. In the electric motor the electric current direction is switched back and forth rapidly to spin the motor at high speed. In this investigation you will create a simple electromagnet using a metal nail, ordinary wire, and a battery.

 
Part 1: Build the electromagnet

Connecting the electromagnet to a battery deflects a compass needle
  1. Cut a long piece of wire, approximately 1 m in length. Strip the insulation off of the two ends of the wire.
  2. Starting about 10 cm from one end of the wire, wrap the wire tightly around the nail. Start from the head of the nail. As you wrap the coil, make sure it is tight and that the wire does not cross itself.
  3. Stop wrapping at a point 0.5–1.0 cm before you get to the tip of the nail. You should have at least 10 cm of free wire on this end of the nail.
  4. Attach the wire from the tip of the nail to the positive terminal of the battery. Attach the other end of the wire to the negative terminal.
  1. Does your electromagnet deflect a compass needle?
  2. How many paper clips can it lift?
  3. Propose additional investigative questions: What variables could you change that might affect the strength of your electromagnet?


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Part 2: Determine its polarity

What is the polarity of each electromagnet?The polarity of a magnet indicates which end is north or south.
  1. Using a model including the right-hand rule, predict the polarity—which end is north and which is south—of your electromagnet. Justify your answer. (Hint: Inspect carefully how you wound the wire around the nail and include that information in your model.)
  2. Using the compass, check your prediction. Were you right?
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