Another story

Back in the late '60s an IBM CE related this story to a number of us on a break.

He was fascinated by magnetic repulsion.  You've probably seen the demonstrations where an aluminum slug is placed on a steel rod with a magnetic coil at its base.  Alternating current is applied and the slug floats a distance up the rod even though it has no intrinsic magnetic properties.

He wanted to build a magnetic repulsion cannon based on that demonstration, and began collecting the needed supplies.  He started with big capacitors.  They came from computer mainframe power supplies that were being junked.  He collected a number of them, sixteen perhaps (I think he said he had a farad of capacity), and connected them together in parallel using heavy wire, then attached the lot to a trickle charger.  He said that after a week they were three quarters full.

Other parts of the circuit were a spring loaded six inch long copper knife switch, a couple loops of 1/4" copper tubing, steel rod, slug and necessary supports.  He placed a blocking piece of wood under the switch handle -- the spring would close the switch when the block was removed -- and connected the rest of the circuit.  He set up the rod to point out of his open apartment window being sure to aim it so the slug would not hit anything nearby.

All was ready.  He got down behind his kitchen counter and yanked the string to pull the block from the switch.

Ker-blam!  A green cloud roiled around and over the counter.  He rushed through it to the window and saw everyone around the courtyard pool looking up at his window where the green cloud was coming out.  He looked at the apparatus and found the slug off the rod by an inch or two.  He looked at the switch -- and the blade wasn't there.  It had vaporized in the arc that had started at the initial contact during closing.

H e was puzzled a bit by this and sat down to do some calculations.  They explained it all.  He had unleashed the equivalent of a megawatt of energy in less than a millisecond.  

A high power, high value resistor was placed across the capacitor terminals to discharge them and the apparatus was broken down and discarded.  His dreams of a magnetic cannon disappeared too.