Making an Electroscope

We've all experienced a shock at some point in the winter, when reaching for a doorknob after walking across a rug. Believe it or not, this shock means you experienced an electric discharge of thousands of volts! Static electricity builds up when materials rub against each other, such as the rubber soles of your shoes against the rug.

Rub a balloon against your hair or a sweater, and stick it to the wall. It is held there by the force of static electricity.

Electrons (subatomic particles that have a negative charge) rub off from one material to the other, causing a buildup of charge. When you rub your shoes against the rug, electrons are transferred from the rug to your body, giving your body a negative charge. When you reach for the doorknob, the electrons jump from your hand to the knob, causing you to feel a shock. Static electricity can be hundreds of thousands, even millions, of volts.

You can get a shock of half a million volts without harm in the winter just from electricity. How can you live after such a shock? It's amperage (current) that kills you, not voltage. Dangerous electric sources, such as a wall outlet or lightning-another form of static electricity-have high electric current.

An electroscope is a device that shows the presence of electric charge. It contains a delicate piece of metal foil that moves when electrons flow through the electroscope. You can build an electroscope to investigate the electric charges in various materials.

Materials

• metric ruler
• marker
• thin piece of aluminum sheet metal (Scrap aluminum siding works well for the walls of your electroscope. You can sand it down to the shiny bare metal if it is coated.)
• safety goggles
• tin snips
• coffee cup
• duct tape
• epoxy
• aluminum foil or steel wool
• drill and bits (requires adult help)
• cork or rubber stopper
• scissors
• gold leaf (from an art store), platinum lead (from an electronics store or science supplier), or aluminum foil (from a gum wrapper)
• two 8-by-12-cm pieces of Plexiglas
• Lucite and glass rods
• wool and polyester remnants

Procedure

To Make the Electroscope

Use tin snips to cut the parts out.

Wear safety goggles with side shields when cutting, drilling, or otherwise working with metal.

1. Measure and mark with a marker on aluminum sheet metal the dimensions of the following parts.
   1. Two sides that measure 6 by 12 cm each.
   2. A base and a top that measure 8 by 6 cm each.
   3. A disk that measures 6 cm in diameter. (Hint: You can trace the bottom of a cup to make the outline of your disk.)
   4. A rod that measures 8 by 1 cm.
2. Attach the sheet-metal rod perpendicular to the center of the metal disk, using duct tape and/or epoxy. Make sure they are in electrical contact—that is, bare metal of each piece should be touching.
To make a good contact, you can use aluminum foil or a clump of steel wool at the junction between the rod and the disk.
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4. Have an adult first drill a l-cm hole in a cork, then drill or cut in the middle of the top piece of the electroscope a hole that is big enough to hold the cork firmly.
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6. Pass the rod through the hole in the cork so that 3 cm of the rod sticks out above the cork and the remainder hangs below. The rod should fit snugly inside the cork. Fasten the rod to the cork with epoxy if it is too loose.
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8. Cut a 2-cm-long strip of foil from gold leaf. Attach one end of the foil 2 cm from the free end of the rod, using a tiny drop of epoxy, so that the foil is hinged to the rod.
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10. Assemble the electroscope, using the metal sides, base, and top, and two 8-by-12-cm pieces of Plexiglas. You can use epoxy and/or duct tape to hold all the sides together except the top. Use only tape on the top, in case you need to remove it for adjustments.
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