Charge and Carry
| When a Styrofoam
plate is rubbed with a wool cloth, it becomes charged negatively.
That's because the Styrofoam attracts electrons from the cloth.
Often, a plate fresh from the package will start with a positive
charge. If it does, it will have to be rubbed long enough to cancel
this initial charge before it can begin building a sizable negative
charge. When the pie pan is placed on the Styrofoam, the electrons
on the Styrofoam repel the electrons on the pan.
The electrons can't leave the pie pan because it is completely surrounded
by insulating air and Styrofoam, so the pan retains its neutral
charge. If a visitor touches the pie pan while it is near the Styrofoam,
the mobile electrons will be pushed off the pan and onto the persons
body. The electrons make a spark as they jump a few millimeters
through the air to reach the finger. The air in the spark is ionized
as the moving electrons knock other electrons off air molecules.
The ionized air emits light and sound.
After the electrons leap to the users body, the pan has a
positive charge. Physicists say the pan has been charged by induction.
The pan can be carried around by its handle, bringing the positive
charge to other objects. If the positive pan is brought near any
object that can be a source of electrons, the pan will attract electrons,
creating a second spark.