Detecting Magnetic Fields
The third lab activity is designed to introduce students to the connection between electricity and magnetism. Students reenact Hans Oersted’s original discovery by placing a compass adjacent to a current carrying wire. This activity represents a crucial experience in the sequence of the FabNet Invention Kits as this discovery was used in many later inventions.
What is the relationship between electricity and magnetism?
- battery clip
- magnet wire
- alligator clips
- lighter, scissors, or emery board
Magnet wire is coated in a red enamel paint that insulates itself. Instead of using wire strippers, you can use a lighter to burn off the enamel coating. You do not need to hold the wire under the flame for very long – one second under the flame should remove the coating. Alternatively, you may use scissors or emery board to scratch the coating off.
Expose enough wire to connect an alligator clip to each end of your magnet wire.
Connect each end of the wire to the positive and negative battery terminals. Keep the battery at least six inches from the compass to avoid interference. Position the wire so that it is aligned with the north and south poles of the compass.
How does the wire affect the compass needle when the circuit is disconnected?
Tap the alligator clip to the exposed end of the magnet wire. Do not leave this connected for more than a couple of seconds. The wire will get very hot and burn your hand if you are not careful.
How does the wire affect the compass needle when the wire is connected to the battery?
Now reverse the connections from the battery to the wires using the alligator clips. The battery has two terminals, one positive and one negative. Make sure you change the orientation from the previous step. Perform the same experiment as in the previous step.
What do you observe? How is this different from what you observed in the previous step?
Now place the wire under the compass. Connect the wire up to the battery in the original orientation (not reversed).Your circuit should look similar to the image on the left. Perform the same experiment as before.
How does the compass needle move when the wire is underneath the compass? How does this compare to when the wire was above the compass?
Now reverse the connections from the wire to the battery, just like we did when the wire was above the compass.
What do you observe? How does this experiment compare to when the wire was above the compass? Can you think of an explanation for what you observed?