- Glass Jar or Glass
- Aluminum Foil
- Index Card
An electroscope is an instrument for detecting the presence of static electricity. It consists of two thin metal leaves suspended from a metal hook. When the hook is brought near a source of static electricity, some of the electrons in the hook are pushed to the leaves (if the source is negative) or pulled up to the hook from the leaves (if the source is positive). Either way, the leaves are now charged the same way as each other and so they repel each other. The amount they open up is proportional to the charge of the source (if the sources are always held at the same distance from the hook).
Cut two strips of foil lcm by 4cm (1/3″ by 1 1/2″) Open out the paperclip to form the shape at right. Push the hook through the middle of the index card and tape so that it is at right angles to the card. Lay the two foil strips on top of one another and hang them on the hook by pushing the hook through them. Lay the card over the jar so that the strips hang inside.
Bring various charged objects (the balloon rubbed on students’ head) near the hook and observe what happens. Notice what happens to the strips when the sources are removed. Does anything different happen if the source actually touches the hook? If the strips do not fall back together, gently touch the hook with your finger.