Static Electricity
Atoms have two types of particles with charges:
Protons (positive) in the nucleus. Protons stay in the nucleus.
Electrons (negative) on the outside. Electrons can move from atom to atom.
The charges are exactly opposite, the charge on 1 proton is exactly opposite to the charge on 1 electron.
In neutral substances (no charge) the number of positive charges is equal to the number of negative charges.
Making Static
Some substances hold their electrons loosely. Some substances hold their electrons very tightly. The following
are listed in order from most attracted to electrons to least attracted to electrons.
Air
Balloons (rubber)
Protein (silk)
Protein (wool)
Plastic (plexiglass)
Water
Aluminum
Copper
Gold
When substances with different attractions for their electrons move past each other, electrons can be taken off of
one substance and put onto another. If the substances do not allow electrons to move easily, the electric charges
will stay in one place--static electricity.
Static electricity is an electric charge which builds up in one place. The definition of static is not moving or
stationary.
Polarity
Polarity describes what the charge is: positive or negative.
The substance that gains electrons off the other substance will have extra electrons and negative charge.
The substance the loses its electrons will have less newtons than protons, and a positive charge.
Conductors and Insulators:
All materials conduct electricity, some conduct electricity very easily, some do not conduct electricity very well
at all.
Good Conductors
Poor Conductors (insulators)
metals
air
water (better with dissolved solids)
rubber
salt
plastic
glass
Conductors: When we say a substance is an electrical conductor, we mean it is a good conductor.
Insulators: When we say a substance is an insulator, we mean it is a poor conductor.
Static charges build up on poor conductors because once the charge has happened, the charge cannot move off
of the poor conductor.
Charge Transfer
Static charges can transfer from a poor conductor (like rubber or plexiglass) to a good conductor (like aluminum
foil). If the good conductor is touching only poor conductors, the charge cannot escape off the aluminum foil
easily.
Charge Behavior
Charges that are different attract (pull toward) each other. Positive attracts negative, negative attracts positive.
Charges that are the same (like charges) repel each other.
Induced Charge
A substance with a static charge can induce (cause) a charge in another substance.
Example: The negatively charged balloon repels the electrons in the pieces of kleenex. The electrons move the
edge of the kleenex farthest from the balloon causing an induced negative charge on the edge of the kleenex
piece with extra electrons. The other edge of the kleenex is positive because it is missing electrons. Opposite
charges attract, so the kleenex sticks to the balloon because of an induced charge.
Electricity measurements:
Volts (V): measures the strength of the charge--how much force is on the electrons to move. Static electricity
can build up very large voltages. 30,000 V is not uncommon.
Amps (A): measures the size of the charge--the total number of electrons in the charge. Static electricity can
have very tiny amounts of amps--shoes on carpet, or very large amps--lightning.
Ohms (): measures resistance--how easily or hard the electricity can move.
Static Discharge:
When the voltage of a charge is greater than the resistance of the substances which separate the charges, the
electrons will jump. This is known as static discharge. Air will allow static discharge when the voltage is more
than 3,000,000 V / meter of air (30,000 V / cm of air); the air breaks down and allows electricity to flow.
When air breaks down, electrons are stripped off of the air molecules--this is called ionization. The ionized air
molecules form a path that the static charge can flow through. When the electrons return to the air molecules,
light is given off--a spark. The air molecules become super heated and expand--causing the snap you hear. Most
static discharge is very high voltage, but low amperage, so it does not cause any permanent damage.
Uses of Static:
Photocopy machines use static electricity to put the toner on the paper. The heart of a photocopy machine is a
drum made of special metal which looses its charge when exposed to light. Dry powdered toner (ink) sticks to
the parts of the drum which still have a charge. When paper is rolled across the drum, the toner sticks to the
paper. The paper is then sent to the finisher which applies heat to seal the toner to the paper. Laser printers
operate the same way, but use a laser beam to change the charge.