Accidents happened and we had a few in the April issue of Science Scope!
A note on plastic bags: Oven roasting bags work best, and a few kinds of trash bags are OK. If you arenít feeling very experimental, stay with the oven roasting bags, which work extremely well. Many plastic bags simply will not work, or produce such a tiny charge that it is hard to do the rest of the experiment.
The pictures of the electrophorus:
Under hint 2: The pan is neutral, charge separation is caused by the repulsion of the negatives and attraction of the positives to the negatively charged board. So, there should be equal numbers of positives and negatives on the pie pan!
Under hint 4: The charges donít spread out until you move the pie pan away from the cutting board, and when they do spread out, there arenít any more of them, the just spread farther apart.
About the electroscope: You must use bare wire for the electroscope, or charges wonít be free to move from the wire to the foils. I usually just use a paper clip, since they are almost always available. I unfold it in the middle so it looks like an "S" and use the small end on top and the big loop to put the foils on. I then make sure the ends of the wire are bent back in to the middle, and try to trap this place in the hole in the cap. If you have free ends sticking out loose, you lose more charge. You can also just wrap a piece of electrical tape around where you bend the ends together to keep them tight. If you do use regular wire, instead of the paper clip, make sure it is un-insulated. A lot of wire looks bare, but has an insulating varnish painted on it. One test you can make if you are not sure: if you run sandpaper over it and it changes color, it is insulated!