Electricity and Magnetism

Objective: To demonstrate how magnetic fields interact with each other and electrical current.

Materials needed:
• coil
• power supply and/or battery
• some permanent magnets (poles marked)
• magnet holder
• electro-magnetic wand
• multimeter
• iron filings
• plastic platform
• tranparency of earth
• video camera (for large classrooms)

Demonstrations:

With these materials multiple related demonstrations that are listed below can be made.

The earth's magnetic field: Take the plastic platform and place it on an overhead projector, centered on top of one of the larger of the permanent magnets. Then place the transparency with the earth over the magnet, so that the earth's magnetic poles line up with the magnets poles. Liberally sprinkle iron filings on top of the transparency. To help get them to spread out evenly among the magnetic field lines you can firmly tap the top of the plastic platform. When you are done, simply pour the iron filings back into the bag from the transparency.

Magnetically induced electric current: Wire the coil into the multimeter, one wire into galvonometer and one into ground. By pushing a permanent magnet into the coil the needle on the multimeter will deflect one direction; and by turning the magnet around or pushing it out the other side of the coil the needle will deflect the other direction. The same can be done with the em-wand while it is attached to the battery/power supply. (Show that without em-wand hooked up to a current, nothing will happen.) If you use the power supply, then you can hold the em-wand inside the coil and turn the voltage up and down on the power supply to show that this generates current in the coil just like physical movement.

Magnetic deflection: Place a permanent magnet in the magnet holder (it should align itself to magnetic north). By rythmically bringing another permanent magnet, or the powered em-wand, close to the one on the holder you can get the magnet on the holder to spin (being a motor with your hand takes some practice). Hooking up the coil to the power supply and setting the magnet on the holder nearby one end of the coil, you can open and close the circuit to deflect the permanent magnet on the holder. Also, you can place a permanent magnet inside the coil while the power is off, then turn the power on and watch the magnet fly out of the coil.