next up previous
Next: About this document ...

Fun with Magnets

Read and do the exercises on pp. 430-434 of the handout.

We have seen that a current exerts a force on the magnetic needle of a compass. This also works the other way around; the magnetic field produced by a compass exerts a force on an electric current. Convince yourself of this by doing the following:

First, convince yourself that your wires aren't attracted to the magnet. You'll find that the alligator clips, on the other hand, are attracted to the battery.

Make a circuit of two batteries and a few pieces of wire. (Don't hook it up yet, or you'll run down the battery!)

Hang a length of the wire off the table so it can swing freely. To get a long enough piece of wire, you'll probably need to string a few of the wires together. See the figure on p. 497.

Place a magnet near the wire (but not the alligator clip). Then briefly complete the circuit. Do you notice the wire jump? Don't keep the circuit closed for long, or else you'll drain the battery.

Conduct several such experiments with different poles of the magnet and with the battery poles reversed. For each trial, not the direction of the current, the direction of the magnetic field, and the direction of the force on the wire. The direction of the force might be difficult to see.

If you can, come up with a theory that related the direction of current, the direction of the field, and the direction of the force. (This might be hard; don't worry if you can't.)

Do magnets interact with electrically charged objects? Do some experiments with invisible tape and draw a conclusion. (Remember that neutral objects will be attracted to charged objects.)

Do the exercises on p. 112 of the handout. Supplies should be in the lab -- if not, ask Don Cass. Trivia question: what is the name for the device you've built?

next up previous
Next: About this document ...
David Feldman