Dr. Frankenstein is giving a VIP tour of his laboratory, deep in the caverns below a Transylvanian castle. His equipment is old, but crafted with great care and scrupulously maintained.

With the tour group is a young EE from a fancy university who is scornful of everything. When Dr. Frankenstein shows his 100kV voltage generator, the student sneers, "At the University, we have a supply that delivers a megavolt!" When the doctor shows a huge analog computer with hundreds of op amps made of discrete transistors, wired to simulate neural waveforms, the student talks at length about superiority of the computer networks he has configured.

The doctor calmly continues the tour and walks over to a bench with a very simple setup. Everything is constructed with great care and precision. The connections are gleaming brass and everything is mounted on a beautifully finished mahogany board.

Figure 1

There is a black box with two terminals, connected as shown in Figure 1. A voltage source is set to 1VDC. The resistor is a standard, wire-wound 1-ohm, 10-watt resistor. The meters are traditional old-fashioned d'Arsonval meters. The voltmeter shows 0.5V and the current meter shows 0.5 ampere. But the black box does not get warm!

"Can you explain this?" asks Dr. Frankenstein. The young student accuses the Doctor of fraud and takes some measurements using the latest pocket VOM. He confirms the reading and finds that the voltmeter draws negligible current and the current meter drops negligible voltage. He declares that this is impossible. "It's some kind of trick!"

You and the doctor exchange knowing glances and you say, "It's tricky, but it's not a trick. I can identify what's in the box."

Can you?

The usual black box rules apply (no hacksaws, x-rays, etc.).

— Contributed by Charles Ratcliffe, Sancrafter Co.

Answer