Measure Static Electricity With An Electroscope!
Summary
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 making a simple, 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
- Cut a 3-inch piece of the straw.
- Trace the opening of your jar on the cardboard and cut out the resulting circle.
- Punch a hole through the center of the circle that is big enough to fit the straw through.
- Insert the straw into the hole and firmly secure it with hot glue.
- Cut the straight part off the metal coat hanger.
- Use the pliers to twist one end of the wire into a spiral.
What do you think is the purpose of this spiral?
- Insert the straight end of the wire through the straw and create a small hook on the other end of the wire.
- Cut out two drop-shaped aluminum pieces, about 1-2 inches long. At their top, cut out a small hole.
- 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?
- 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
- 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?
- 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?
- Now, remove the Styrofoam from the vicinity of the wire.
What do you notice?
- 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?
- 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?
- 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
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.
Digging Deeper
Static electricity is the buildup of electrical charge on an object. This charge can be suddenly discharged (such as when a lightning bolt flashes through the sky) or it can cause two objects to be attracted to one another. Socks fresh out of the dryer that cling together are a good example of this attraction in action. Specifically, static cling is an attraction between two objects with opposite electrical charges, one positive and one negative.
Static electricity can be created by friction such as rubbing one object against another object. This is because of the rubbing negative charges, called electrons, are released which then can transfer between objects to produce a static charge. Depending on if the object loses or gains electrons due to the electron transfer, the object's charge becomes either positive (the object loses electrons) or negative (the object gains electrons). For example, when you shuffle your feet across a carpet, electrons can transfer onto you, building up a negative static charge on your skin. You can suddenly discharge the static charge as a shock when you touch a friend or some objects.
Whereas objects that have opposite charges are attracted to one another (such as clingy, freshly-dried socks), objects that have the same charge repel. This principle is used in making an electroscope, which is a scientific instrument that detects electrical charges. The wire inside the electroscope is a conductor, which means that electrons can move freely inside the material. When a charged object comes close to the wire, electrostatic induction happens. This means that the electrostatic charge of the object affects the charge inside the metal wire even though they are not touching. A positively charged object attracts the electrons inside the wire and they get pulled up into the metal coil. As a result, the aluminum pieces at the bottom of the wire are both left with a positive charge. A negatively charged object repels the electrons in the metal coil and they get pushed down the wire into the aluminum foils. This time the aluminum pieces are both left with a negative charge. In both cases both of the aluminum pieces are left with the same charge and they start to repel each other. Once the charged object is removed from the vicinity of the metal coil, the electrons move back to their positive charge counterparts. The metal becomes neutral again and the aluminum pieces come back together.
However, if you touch the metal coil with a charged object, electrical conduction happens, which means that electrons can flow from one object to another. For the electroscope this means that any excess electrons from a negatively charged object will flow into the metal wire. This creates a negative charge inside the wire and the aluminum pieces will continue to repel each other even if the charged object is removed. A positively charged object on the other hand will remove electrons form the wire as they flow into the object to neutralize its charge. This leaves the wire with a positive charge and the aluminum pieces will stay separated until the wire is neutralized again.
Ask an Expert
For Further Exploration
- Use your homemade electroscope to test even more materials. Which ones can hold a static charge and which can't?
- You can also use your electroscope to investigate which materials conduct the most static electricity. This is because the farther apart the aluminum foils move from each other, the bigger the charge from the test material is. Which common household materials can build the greatest electrical charge; which ones the least?
- Some objects become negatively charged and other objects become positively charged with static electricity. Try to discover a way to investigate this. Does this kind of electroscope detect both types? How can you tell the difference between the two?
- Static electricity is not good when it gets in your clothes! Try an experiment rubbing an object with a dryer softener sheet (such as Bounce) after rubbing the object against the piece of wool. How do dryer sheets work? What happens to the electroscope reading after rubbing a charged object against a dryer sheet? How do different dryer sheet products compare?
Related Resources
Project Ideas
Links
- Science Made Simple: What Is Static Electricity?
- Ron Kurtus's School for Champions:Effect of Materials on Static Electricity
- KidsHealth: Why Do I Get an Electric Shock?
- Bozeman Science: Electrostatic Induction
