A - A very "strong" horseshoe magnet - Alnico - rests upright on the table and a flexible electric lead (wire) lies innocently within the jaws of the magnet. We connect the ends of the wire to a 6-volt battery. Instantly the wire JUMPS out of the magnetic field! A very simple but pretty demonstration of the enormous forces arising in the interaction of magnetic fields. A "rule of thumb" can be given to show the relation of the F (Force) - the B (flux) -the I (current) leading to what I call the FBI RULE!
B - A dramatic array of things can be shown by a crude assortment of coils and stuff: A typewriter roller has many turns of wire wound on it. The hole in the roller is filled with soft iron wire. The coil is energized on 110 volts 60-cycle AC. The alternating current gives rise to a changing magnetic field in the region of the coil. Closed copper rings held over the coil experience enormous repelling forces. By induction they are quickly heated. Lamps can be lighted without ANY physical connections. Water can be instantly boiled in a closed copper loop. This device can be made literally out of junk but demonstrates abundantly the wondrous things arising in the study of electromagnetism.
C - We first show that an Al disk is NOT magnetic. .. at least for the magnetic forces ordinarily available to us. The disk is mounted on a central vertical pin. A strong Alnico horseshoe magnet is held by a cord over the disk - symmetrically. The cord is twisted up to store some "twist-energy" in it. As the cord untwists the disk takes up rotation! Strange business! Some say - ah ha - it is dragged along by the viscous friction of the air. No - it is not so. The moving magnet induces in the metal plate an emf. This emf gives rise to a current. This current produces its own magnetic influence. The interaction of the magnetic fields produces the rotation. This disk is known as Arago's Disk.
D - Another Al disk is mounted on a central vertical shaft. The disk is given a spin and we note its spin-life...how long it spins. Now we bring up to the plate - the Al disk - a strong horseshoe magnet whose field envelopes the rotating plate. The rotation of the plate is nearly instantly arrested. Again we see the interaction of the field due to the permanent magnet with the field due to the current arising in the rotating plate. It is as if one hand washes the other!
E - In a playful mood we reproduce one of Faraday's delightful experiments which he did for the children in his Royal Institution Lectures: We throw some nails at random onto a magnet resting on the lecture table. The nails are forcefully grabbed by the field and they all take up positions representing the lines of flux between the poles. Faraday used iron filings and the "tunnel" which grew in this playful action was "just right" - he said - "for a little mouse to pass through". Our beloved Faraday.
Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.
This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.