Making Small Change Smaller

Bert Hickman, a retired electrical engineer living outside Chicago, enjoys using magnetic force to smash coins to roughly half their normal size.

Bert’s high-voltage equipment takes up most of his screened-in porch (from the looks of things, his wife drew a line at the sliding door — there’s a clear border between tidy suburban house and chaotic suburban lab). Bert begins the coin-shrinking process by wrapping a quarter in copper wire and bolting the leads to copper bus bars, which are connected, by way of a triggered spark gap, to a 600-pound bank of 12,000-volt capacitors. A bulletproof blast shield encloses the coin and coil, and a high-voltage power supply charges up the capacitors. The only thing holding back the several thousand joules of energy stored in the capacitors is the tiny space between the spark gap’s two brass discs.

Pressing a switch triggers the spark gap, which releases the entire charge through the coil in 25 millionths of a second. This creates a huge magnetic field, which induces a current and then a magnetic field inside the coin, which in turn pushes back against the field outside. The repulsion force between these two fields crushes the metal, instantly taking a quarter down to the size of a dime. A large amount of energy discharged in a short amount of time usually entails an explosion, and in this case the copper coil is blown apart with a brilliant flash and a satisfying bang.

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