In this activity, we will use some wool to make sparks fly.
You will need
A Styrofoam cup.
An aluminium pie-plate.
A piece of Styrofoam about the same size as the plate. I used a piece of packing foam, but you may also find a Styrofoam plate works well.
A woollen jumper or rug.
What to do
This activity will work best on a cool, dry day.
Using the sticky tape, attach the cup, upside down, to the middle of the inside of the aluminium plate. This makes a handle you can use to hold it.
Rub one side of the Styrofoam against the wool for about a minute.
Place the piece of Styrofoam on the table, with the side you rubbed against the wool facing upwards.
Using the cup as a handle, place the aluminium plate on top of the Styrofoam.
Touch the edge of the plate with your finger. You may hear a crackling sound and feel a spark jump from the plate to your finger.
Lift the plate up, using the cup as a handle.
If you bring your finger (or someone else's) close to the plate, it will produce a spark between the plate and the finger.
You can make more sparks by repeating steps 4 to 7.
If you try this activity in a darkened room, you should be able to see the spark jumping from the plate to your finger.
All matter contains particles with an electrical charge. Normally, the number of positive and negative charges is the same, so they cancel out. This is called a neutral charge. Sometimes, when you rub things together, some of the negatively charged particles (called electrons) will move from one object to the other, so one will have more positive charges and one will have more negative charges. This build-up of charge is what we call static electricity.
The activity relies on two principles. The first is the way that charges attract and repel each other:
Particles with the same charge repel each other.
Particles with the opposite charge attract each other.
The second is the way that electrons can move through a material:
The aluminium plate, like all metals, is a conductor. This means electrons can move though it easily.
Styrofoam is an insulator, which means electrons can't move through it easily.
To begin with, everything in this activity had a neutral charge. When you rubbed the Styrofoam against the wool, some of the electrons in the wool move to the Styrofoam, so the foam gains a negative charge. Since the foam is an insulator, the extra electrons stayed in the part of the foam you rubbed against the wool.
Particles with a similar charge repel each other, so when you placed the aluminium plate on the Styrofoam, the electrons in the plate were repelled by the electrons in the Styrofoam. Some of the electrons were able to move through the metal to go as far away from the foam as they could. When you touched the plate, these mobile electrons travelled through you. They may have even travelled through the air to reach you, producing a spark.
Since the plate had lost some of its electrons when you touched it, it ended up with a net positive charge. Once you picked it up, if you brought it near something with a neutral or negative charge, the electrons in the other object would be attracted to the plate. If you brought it close enough, some of the electrons could jump through the air to reach the plate, producing a spark.
Laser printers and photocopiers use static electricity to transfer black dust called toner onto paper. When the toner is heated, it sticks to the paper and forms the image. How Stuff Works has a good explanation of how photocopiers work.
Some industries use static electricity to remove soot and ash from their emissions, so they produce less pollution.
Tape the cup to the plate.
Rub the Styrofoam against the wool to charge it up.
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