# Homework Help: Black Box Enigma

1. May 3, 2005

### xiuxiu

I was recently given a physics lab and it's very hard for me to complete. We were shown a demonstration in which some unknown object was in a "black box." There was a wire leading from the box that was plugged in, thus the object was charged. A light bulb was led around the box. Then, at the top of the box, the bulb (with wires or some magnetic base maybe on the bottom?) lit when it reached the top of the box. The farther the lightbulb got from the box, the dimmer it became. I have a few ideas, but can't seem to come up with a working hypothesis. I think the object might be a transformer, some sort of tesla coil, or maybe some sort of broadcast-type object which can transmit electricity. So far, nothing I have come up with is capable of just transmitting a small charge to a small lightbulb through the air.

2. May 3, 2005

### OlderDan

Your ideas are probably going in the right direction. The something on the bottom of the bulb could be just a wire loop, or coil of wire connected to the inner and outer connector of the bulb. What happens in a coil of wire if you change the magnetic "flux" through the coil? Three crossed coils would ensure that one of them is always lined up right to get some effect. But it could be made direction dependent, so if "led around the box" means no light there, a directional selection effect was probably at work.

3. May 5, 2005

### xiuxiu

Thanks. I don't know what happens if I change the magnetic flux through the coil? We were only given one demonstration. Anyway, I ended up handing it and I said it was a coil of wire with a magnet inside of it. I stated that some machine moved the magnet back and forth through the coil... haha I had no clue...

4. May 5, 2005

### xiuxiu

Ohh... If you change the magnetic flux, doesn't it reverse the direction of the current? So... sorry about that last reply... haha I'm still lost?