Teaching Notes

To help students understand electric and magnetic fields, students can take the side excursion on Fields available on the CPU Simulation Activities CD. Directions to the students, teacher notes and designed simulations are available on that CD. This side excursion is designed to follow What Do You Think? on page 264.

In Step 1, point out to the students that they should avoid actually touching the magnet to the compass, since the magnet could demagnetize the compass needle. In Step 4, if the students cannot see the effect, suggest they take a longer piece of wire, wind a coil around their hands, and put the compass in the coil. When they touch the ends of the wires to the battery, the deflection of the compass should be unmistakable. In Step 6, the students turn the wire to different directions and watch what happens to the compass. Note that when the wire is pointing west-to-east, its magnetic field will then point north-to-south or north-to-south. If the students orient the battery poles so the magnetic field is also pointing north, then the compass will not deflect, since it is already pointing north. Hold off on handing out the batteries until the students have finished with the galvanometer see (Advance Preparation and Setup). In Step 12 the students connect several batteries together end-to-end. Note that these batteries must be pointed in the same way, so the plus end of one is up against the minus end of the next. Otherwise the batteries will cancel each other out.

Many students, if not most, are unfamiliar with the magnetic field of a current-carrying wire. For these students further experimentation, such as finding the effect of a current-carrying coil of wire on a compass, can help. Some students believe that rubber insulation prevents a wire wrapped around a nail from creating an electromagnet. Asking students to predict the result with insulated wire, and then doing the experiment, can help with this preconception.