Electroscope Materials

Because gold is infinitely mallable and can be made VERY thin. If you've ever handled gold leaf, you'll see why. The idea is for the hinge point to be very flexible and the moving surfaces to be very light.

Incidentally, you can get gold leaf at any art store. Just be VERY careful how you handle it. Two sheets will permanently weld themselves together if they touch.

In college, we tried to make a real gold leaf electroscope. We finally got it working and found it amazingly sensitive. We could detect a charged toy ballon at about 3 meters. However, we wrecked a considerable quantity of gold leaf before we were able to produce a working electroscope. The main purpose of the glass jar is NOT for electrostatic isolation. It's to keep slight air movements from trashing the gold leaf.

Yep.

Yep.

Thin Al foil from a chewing gum wrapper works ok. See:

Search Google for "aluminum foil electroscope". Aluminum is MUCH easier to handle than gold, but because it weighs more, is less sensitive.

assorted stuff ... and then:

Aluminum is MUCH

Huh? Aluminium weighs more than gold? Am I in the wrong universe?

Chris

Meep!

I said weight, not specific gravity or density. Hammered gold leaf is about 0.1 micro meters thick. Aluminum foil that thin would just crumble or shred itself. I think the best I can find for aluminum foil is rolled (not hammered) at about 1,000 micro meters thick. That's about 10,000 times as thick as gold.

The electrostatic forces on each leaf are repelling each other, but are also fighting gravity. The flexibility and weight of the material is a key part of how much they move and thus their sensitivity.

I errrrred. 1,000 micrometers is about the thickness of the paper backed aluminum foil on the gum wrappers. It is possible to buy pure aluminum leaf down to about 15 micro meters thickness. That would get the weight down to something comparable to gold. However, there's a problem. The aluminum leaf is substantially stiffer than the gold version, thus reducing its sensitivity. Aluminum leaf will certainly work (I haven't tried it), but gold is probably better.

I got some email asking what keeps the two leafs of the electroscope from sticking to each other permanently? There two leafs are part of a single conductor. In order for them to stick, it would be necessary to have opposite charges on each leaf, which is impossible. There's always a small surface electrostatic charge to keep them slightly apart and prevent welding. However, if the two leafs were insulated from each other, welding would certainly be a problem.

Don't ask me where to find the red squirrels used to make the gilders brushes.

Fizzix lecture on electroscope (9 mins):

Note that the electroscope in the video deflects when the charged plastic gets within about 2 cm of the top electrode. The one we built in college would detect a similar piece of plastic at about 0.5 meter and a balloon at about 3 meters. Ambient radioactivity and cosmic rays were a measurable source of error. Sorry, no photos.