Making a Leyden Jar and Static Zapper

This could go with a discussion of static electricity, but since we talked about the invention of the Leyden jar when we discussed the history of electricity, we made it on a different day. The Leyden Jar is named after the university where it was first used (you say it "LIE-den" jar, if you are wondering) :) and this Robert Krampf video shows how to make one. It's basically just a device that can store and release a static electric charge---i.e., a simple capacitor. For our Leyden Jar, we covered the inside and the outside of a plastic cup with foil, and then made a long snake of foil coming out from under the inside foil. You charge the jar up using static (we rubbed a balloon over Malachi's hair 40-50 times and touched it to the collector, the ball of of foil at the end of the snake. You cAn hear a kind of crackle as it's working.) and then you can discharge it when you touch your finger, or another foil snake, to the collector ball. It's quite fun to see how much charge you can build up (Robert Krampf says it's 25,000 volts!)

You can even see a tiny purple spark in this picture!

This "zapper" works the same way, but this time it's made with a styrofoam cup and plate and a foil pie pan. Directions for making the zapper are here.

Electric current, Conductors, and Insulators

After static electricity, we went on to current electricity. First we played a game where we showed how current flows (emphasizing the point that it isn't a thing that moves along, but energy--an impulse). Everyone held a stuffed animal and we pretended the animals were electrons. You were only allowed to hold one animal at a time, so when I introduced an extra stuffed animal into the system by handing it to one of the children, they had to hand off their other animal to make sure they still only had one. We passed the "current" along the line, and then talked about how if the energy goes down a line, it has to stop when it reaches the end. But if it goes around in a circle, it can keep flowing and flowing. We also showed how an insulator works---if you insert another person into the circle, and that person CAN hold more than one electron, then when the current gets passed to him, he just holds onto it and it stops. In our game, people who easily pass electrons along are conductors, and people that hold onto electrons (or don't accept new ones) are insulators.

Then we did a lab testing different materials for their heat-conductivity. (Idea from here.) We boiled water, then poured it into identical glass jars that were wrapped with various materials, and noted the starting temperature. We then measured the temperature of the water after 20 minutes to see how much heat was kept in by the wrapping. (Our wrapping materials were foil, bubble wrap, fleece [I put felt on the lab sheet, but I couldn't find my felt so we used fleece instead], cotton cloth, paper bag, wrapping paper, and water---the jar of water was in another, bigger, jar of water.)

Here is the Lab sheet I made for us; feel free to use it.

We had a lot of fun testing these things and even some surprises (the foil was a lot better insulator than we predicted---maybe because of the air trapped in its wrinkles? or its thinness?).