Static Electricity
Electricity is an aspect of one of the four fundamental forces in the universe, the electromagnetic force. It
involves attraction and repulsion between charged particles. The charge comes from electrons (negative) and
the protons (positive).
Atoms are electrically neutral. Because they have equal numbers of electrons and protons, they have no net
charge. If an atom gains or loses electrons, it gains a charge and becomes an ion.
Different elements vary widely in their ability to gain or lose electrons. When one blows up a rubber balloon
and rubs it with wool, electrons from the cloth jump onto the balloon. The generation of charge by friction is
called triboelectrity; forget that word before you continue.
Law of Static Electricity: Like charges repel; opposite charges attract.
Conservation of Charge: Charge is not created or destroyed; it is merely transferred from one system
to another.
Conductors: Conductors are usually metals. Electric charge moves through them relatively easily. The
charge is carried through the material by loosely-connected electrons in metallic bonds.
Insulators: Insulators are non-metal materials like plastic, rubber, and ceramics. Their electrons are tightly
bound in their chemical bonds. Charges can’t go anywhere in insulators because there’s nothing to carry them.
When a charge is placed on an insulator, the charge stays where you put it. When a charge is placed on a
conductor it will immediately spread out over the surface of the conductor.
Charging by conduction: A charged object touches an uncharged object. Some of the excess charges
from one object flow to the other object until they both have the same charge density.
Charging by induction: We start out with a charged object and an uncharged object. Charge is
transferred, but there is no physical contact between the two objects. One cannot charge an insulator by
induction however.
Method One
1
2
3
1. Start with one neutral sphere.
4
2. Bring the rod near the sphere. The electrons on the rod repel the free electrons on the sphere’s surface.
As the electrons try to get as far as they can from the negative rod, they bunch up on the opposite side of the
sphere. If the rod is moved away from the sphere, the electrons redistribute themselves over the surface and
the sphere remains electrically neutral. With the rod close, the sphere is polarized – one side has a positive
charge and the other side has a negative charge. The net charge, of course, it still zero.
3. With the rod near the sphere, touch the opposite side of the sphere with a finger. This “grounds” the
sphere. The electrons, wanting to get away from the negative charge on the rod (like objects repel) flow into
your finger.
4. Take the finger away and remove the rod. The sphere, having lost many electrons, is positive.
Method Two
1
2
3
4
1. Start with two neutral spheres touching one another.
2. Bring the rod near a sphere. Electrons in the sphere move as far away as possible. As long as the rod is
there, the spheres are polarized.
3. Separate the spheres. One has excess electrons; the other lacks electrons.
4. Remove the rod, and the two spheres remain charged.