Reference: EM126
Category: Electromagnetism
Purpose: Demonstration of low voltage, high current conditions.
Description: a) Thompson's ring: an aluminium ring is placed around one leg of the transformer, left unyoked. When current is switched on the ring flies off. Dip the ring in liquid nitrogen to dramatically increase this effect. If the yoke is placed across the poles so that the ring is trapped it buzzes angrily but remains where it is, growing very hot.
b) A small light bulb is connected to a few turn of wire. As these are brought down over one open-yoked leg the light bulb begins to glow. If the light bulb coil is trapped by closing the yoke over it, the light bulb glows much more brilliantly when the transformer is switched on. Do not switch on for more than a second or the light bulb will burn out.
c) A shallow circular ring-shaped tray with a handle contains a little solder. Hold it around one leg with the yoke closed above it. This constitutes a secondary coil of one turn. The large current soon melts the solder, which can be poured out onto a wooden board.
d) Spot-welding: A helix of thick copper rod is connected to handles with terminal clamps for two iron nails. When these are touched together the two nails are fused together.
