# Measure Static Electricity with an electroscope

## Introduction

Have you ever been zapped by a door knob or another person? It feels like a little electric shock and usually happens on cold and dry winter days. Where is this shock coming from? Why is it that sometimes you get zapped and sometimes you don’t? It all has to do with static electricity, which can build up in some materials and then be transferred from one object to another. Sometimes you can even see a spark fly between them! In this science activity you will explore how well materials around the house produce static electricity by a homemade electroscope (an instrument that detects electric charges) and testing it out. The results may shock you

## Materials

• Metal hanger (uncoated) or copper wire (at least gauge 14)
• Glass jar
• Straw
• Scissors
• Cardboard
• Electrical tape
• Hot glue gun
• Pliers
• Piece of Styrofoam®
• Piece of wool
• Optional: piece of wood, plastic bag, tablespoon

## Prep Work

1. Cut a 3-inch piece of the straw.
2. Trace the opening of your jar on the cardboard and cut out the resulting circle.
3. Punch a hole through the center of the circle that is big enough to fit the straw through.
4. Insert the straw into the hole and firmly secure it with hot glue.
5. Cut the straight part off the metal coat hanger.
6. Use the pliers to twist one end of the wire into a spiral.

 What do you think is the purpose of this spiral?
7. Insert the straight end of the wire through the straw and create a small hook on the other end of the wire.
8. Cut out two drop-shaped aluminum pieces, about 1-2 inches long. At their top, cut out a small hole.
9. Flatten both aluminum pieces and hang them on the hook of the wire. Make sure they both touch each other.

 Why do you think it is important that both aluminum pieces touch each other?
10. Place the wire with the aluminum pieces into the jar and tape the lid to the jar with electrical tape. Now you have completed building your electroscope!

## Instructions

1. To test your electroscope, create some static electricity by rubbing the Styrofoam on a piece of wool. Rub the Styrofoam several times with the wool.

 How do you think this creates static electricity?
2. Quickly hold the electrically charged Styrofoam close to the coiled part of the metal wire on your electroscope. Be sure not to touch the wire! Watch what happens to the aluminum pieces inside the electroscope.

 What do you observe?
3. Now, remove the Styrofoam from the vicinity of the wire.

 What do you notice?
4. Hold the Styrofoam against the remaining wire of the metal hanger. Then hold it close to the metal coil on the electroscope again.

 Do you get the same results as before? Why or why not?
5. Charge the Styrofoam again by rubbing it against the wool and this time touch the metal coil with the charged Styrofoam. Then remove the Styrofoam from the coil.

 What happens this time?
6. Repeat steps 1-5 to test the static electricity present in other materials. For each material observe what happens to the aluminum foil inside the electroscope.

 What do your results tell you about the material you are testing? Based on your observations, was the material you tested able to hold a static electric charge?

## Cleanup

Dispose of the metal wire, the cardboard, the straw and the aluminum foil in the trash. The jar can be reused.

## What Happened?

Did both aluminum foils move away from each other when you placed the charged Styrofoam close to the coiled wire? They should have! When you rub a material on the wool, electrons can be transferred from the surface of one material to the other by friction. This means that in case of the Styrofoam your hand and the wool got positively charged whereas the Styrofoam got negatively charged. When you brought the charged Styrofoam close to the metal coil electrostatic induction happened, which means that the charges inside the Styrofoam affected the charges inside the metal wire and the aluminum pieces. As a result, both aluminum pieces started to move away from each other.

When you removed the Styrofoam from the vicinity of the metal coil, the aluminum pieces should have come back together. This is because the charges inside the wire got redistributed into their original positions once the charged object was removed. Touching the metal wire with the charged Styrofoam piece discharged the Styrofoam. This is why the aluminum pieces shouldn’t have moved once you brought the discharged Styrofoam piece close to the metal coil. If you touched the metal coil with the charged Styrofoam piece, you should have noticed that the aluminum pieces kept repelling each other even if you removed the object from the coil. This is due to electrical conduction, which means that the electrons from the Styrofoam got transferred to the wire in the electroscope. Materials that tend to gain or lose electrons include wool, human hair, dry skin, silk, nylon, tissue paper, plastic wrap and polyester—and when testing these materials, you should have found that they moved the aluminum pieces similarly to how the Styrofoam did.