An electroscope is a device that is used to demonstrate properties of static electricity. Static electricity is a phenomenon that takes many forms. It can be an electric shock you can get after walking over a carpet, or it can be a lightning bolt from the sky. The electroscope demonstrates the repulsive force that is exerted between two nearby objects with the same electric charge. In this activity you will learn to make your own electroscope. You won't need any exotic materials for this activity, all that is needed is readily available and can even be found in your house.
First of all you must brush-up your knowledge about static electricity. The following links can help to a large extent; they have been listed according to their level of presentation:
To make an electroscope all you need is listed below:
1. An empty glass jar such as a jam jar.
2. A length of stiff copper wire about 12 cm long (or a large steel paper clip).
3. A sheet of aluminum kitchen foil about 20 cm square.
4. A strip of thin metal foil about 6cm x 0.5cm from a sweet wrapper.
5. A disc of cardboard about 10cm in diameter.
6. A small plug of M-seal putty.
Make a very small hole in the centre of the cardboard disc. Bend over about 1.5cm of the copper wire at one end to make a right angle. Hold the other end of the copper wire between your fingers and thumb and push about one-third of its length through the hole in the cardboard disc. Secure this short length of the wire against the disc with adhesive putty like the M-seal. Roll-up the kitchen foil into a ball about 3cm in diameter and push it firmly onto the unbent end of the copper wire to a depth of about 1cm, taking care not to push the sharp end of wire into your hand. Fold the strip of sweet foil in half to make an inverted V-shape and carefully hook it over the bent end of the wire. Place the whole disc assembly on top of the glass jar with the aluminium ball above the jar and the hooked length of the wire inside of the jar. Ensure that the foil strip remains in place on the hook. You now have your completed electroscope. Now you would want to test it.
All you need to test it is listed below:
1. A piece of silk the size of a handkerchief (or piece of cotton cloth).
2. A PVC plastic rod about 25cm long (or length of hard plastic material).
Introduce a charge on the plastic rod by grasping it at one end and gently rubbing the far end with the piece of silk. Move the charged end of the rod near to the surface of the foil ball on the top of the electroscope, whilst closely watching the behavior of the inverted V-shaped metal strip on the wire hook within the jar. The ends of the strip should move further and further apart as the rod is moved closer and closer to the foil ball. An alternative to the charged plastic rod is a toy balloon. You can charge it up by brushing it against your hair.
The electroscope works best on a dry day. On wet or humid days it might not work at all, because water vapour in the air continuously discharges the static charge that you are trying to create on the rod.
There are many other variations to this simple design. Do you want to explore them? It's very easy! just click on a link listed below and you will come across a new design.