tcepsa | Golden Opportunity

One of my brothers is a glassblower. He's been doing it for several years and, I would say, has become rather proficient. While he was at Iowa State he was able to use their glassblowing facility and supplies to develop his skills, but now that he has graduated he has to rent time at a glassblowing club and provide more of his own supplies. This is why, yesterday, he was opening a package containing several small sheets of gold leaf.

Not being one to let such a chance to reproduce a famous experiment slip through my fingers, I asked if I might use a few small strips of it. After much struggling to extract such strips (gold foil, it turns out, is incredibly difficult to manipulate without incurring unplanned tears) I finally had two pieces about an inch across and three inches long. I know, it's scandalous to be carrying this out and not using metric units, but for my purposes the dimensions were not terribly important. I took a piece of wire and fashioned a little hook at the end by turning it back on itself, and then wrapped the center of the wire around a pen so that the hook was hanging from the pen. Then, with my brother's help, I carefully pierced the hook through one end of the strips, after which I placed the pen across the opening of a glass so that the gold strips hung down into the glass.

There followed a period during which we unsuccessfully searched for a balloon, and settled for using a plastic bag instead. After vigorously rubbing it against my brother's head, we held it close to the top of the glass. The foil promptly swung over and stuck against the side of the glass. Oops. The sheets had gotten stuck to each other in our efforts to get the hook through them, so this wasn't quite the reaction for which I had been hoping. A little careful work with another bit of wire got the strips separated from each other, and we again brought the bag towards the mouth of the glass. This time, the results were exactly what I had hoped for: the pieces of foil separated from each other more the closer we brought the charged bag.

For those of you still with me who aren't familiar with this experiment, the separation of the foil is the crucial bit because it provides support for some of the current theories of electricity, namely fields and how electrons act in them. By rubbing the plastic bag on his head, my brother gave the bag a charge (either an excess or shortage of electrons--let's assume an excess of electrons, which would result in a negative charge). One of the principles of electronics states that if you have an object with a negative charge, it will have a corresponding electrical field around it. When we moved the bag close to the top of the glass, the electrical field around the bag interacted with the electrons in the gold foil, repelling them away from the excess of electrons on the bag. Since gold is an electrically conductive material through which electrons can move with relative impunity, the electrons in the foil all moved towards the ends of the strips at the bottom of the glass.

However, this movement of the electrons in the foil meant that there was an excess of electrons at the lower ends of the foil strips, and they conspired to generate their own electrical fields. These new electrical fields also wanted to repel the excessive electrons in their opposing gold strips (the field from the electrons in strip A pushed on the electrons in strip B, and the field from the electrons in strip B pushed on the electrons in strip A). Normally this force is too weak to actually result in the movement of physical objects, but now the gold foil's delicate nature is to our advantage. Its mass is small enough that the force on the electrons results in the two pieces of foil pushing each other apart. The stronger the field on the bag, the more electrons rush to the ends of the foil and shove at each other, and the farther apart from each other the strips of gold are pushed.

My very own electroscope. I'm so proud! ^_^