EM.6(1) - AN ESTIMATE BY A SPRING BALANCE

A few loops or wire shaped as a triangle hang from a large spring balance. The base of the triangular loops are placed crossing the strong magnetic field of a horse-shoe magnet. A DC power supply is connected to the triangular looops (a lecture ammeter ca also be added to the circuit). The demonstration shows that the force on a current-carrying wire in a given magnetic field varies with the current's magnitude and direction. A switch added to the circuit shows that the direction of the force on the loops change when the direction of the current changes.

EM.6(2) - FARADAY'S MOTOR

A copper disc about 8 cm in diameter is held vertically through its center axis that rests on bearings. The rim of this spin-disc stays dipped on a small mercury pool fitted between the poles of a magnet. The strong horse-shoe magnet is placed so that the magnetic field lines of force are perpendicular to the spin-disc. A power supply is connected to the center of copper spin-disc and to the mercury pool A current will pass from the center of the spin-disc to the pool of mercury. When it passes through the magnetic field, the resulting force will make the spin-disc rotate. If the polarities are reversed, the spin-disc reverses direction too.

EM.6(3) - MECHANICAL EFFECTS ON A WIRE

A long copper wire is suspended vertically by rubber bands in a tall stand (rubber bands hold the wire on both ends). The wire is connected to both poles of a DC power supply. A support at mid-height on the stand holds a U-shaped magnet, such that the wire is perpendicular to the magnetic fields of force. When a direct current moves up or down the wire, it deflects to the sides, depending on the magnet's poles orientation. The wire's deflection is about 2 cm to each side.

EM.6(4) - DC ELECTRICAL MOTOR

It shows the basic principles of electric motors. It demonstrates the conversion of the electrial energy into rotary motion as well as the production of electrical energy from rotary motion. There are two examples available. The small one (Saint-Louis Motor) consists of four-pole armature mounted between the ends of two permanent bar magnets. A 6 V battery will operate it. The apparatus sits on a 10 cm x 15 cm plate.

The large demonstration electric motor and generator is about 40 cm high, 50 cm long and 15 cm wide, and is also operated by a 6 V battery. It has a simple design and bright colors for an effective and clear demonstration.

We also have a simplified motor, made with a styrofoam cup, two paper clips, a piece of wire wound in a few turns, magnets and a 6 V battery. As one taps the contacts of the battery to the paper clips, the loops of wire spin around. The commutator is substituted by the "taping." It is very simplified but it shows the effects of the magnetic field in a current-carrying wire.

EM.6(5) - CONDUCTING RAILS

Two parallel conducting rails about 30 cm long are fastened onto a board. A conducting axle-and-wheels assembly is free to roll along the rails. The rails are placed in a strong vertical magnetic field and connected to a battery. When a current flows, the axle-and-wheels experiences a force and rolls. If the direction of the current is reversed, the axle-and-wheels rolls in the opposite direction.

EM.6(6) - LIGHT-BULBS

A bar magnet deflects the large curly filament of a light bulb connected to a DC power supply. If the bulb is connected to an AC voltage, the filament vibrates strongly.

EM.6(7) - ELECTROMAGNETIC SWING

An U-shaped wire is set swinging between the poles of a strong horse-shoe magnet. The swing is connected to the poles of a 12 V battery. When the current is allowed to pass through the wire, it jumps out of the region between the poles. You can use a switch or just keep the circuit open and touch each pole to show the effect.

EM.6(8) - ELECTRON MOTION IN A UNIFORM MAGNETIC FIELD

The apparatus has a 13 cm diameter helium filled electron tube. This tube is mounted at the center of two 30 cm diameter, 130 turns Helmholtz coils placed about 15 cm apart. The Helmholtz coils provide a highly uniform magnetic field. A beam of electrons is accelerated through the perpendicular magnetic field being deflected to a circular path (initially it is a straight horizontal beam to the side). It is a brightly green colored glowing beam, set against a black background. The apparatus allows one to measure the diameter of the circular path corresponding to the applied voltage and deflecting field.