Basics of Static Electricity
Static electricity is when electrical charges build up on the
surface of a material and stays there (static). It is usually
caused by rubbing two neutral materials together. The
resulting build-up of static electricity is that objects may be
attracted to each other or, even cause a spark to jump
from one to the other. Common examples of static
electricity in action are static cling, fly-away hair and the
sparks that can occur when you touch something.
Questions you may have include:
What causes static electricity?
Why do things attract or repel?
What causes a spark?
This lesson will answer those questions and explain the
concepts concerning finding static electricity.
Cause of static electricity
Static electricity is usually caused when certain materials
are rubbed against each other, like wool on plastic or the
soles of your shoes on the carpet. The process causes
electrons to be pulled from the surface of one material
and relocated on the surface of the other material.
Rubbing a balloon on a wool sweater
creates charges on the surfaces
The material that loses electrons ends up with an excess of
positive (+) charges. The material that gains electrons ends
up an excess of negative (-) charges on its surface.
Electrons pulled from orbit
The gain or loss of electrons can be explained by recalling
that atoms consist of a nucleus of neutrons and positivelycharged protons, surrounded by negatively-charged
electrons. Normally, there are the same numbers of
electrons as protons in each atom.
However, if Object A pulls electrons from their orbit or
shell around the nucleus of Object B, it will cause Object A
to have a negative charge because it has more electons
than protons. Likewise, Object B will have extra protons in
its shell, giving it a positive charge.
Prefers dry air
When the air is humid, water molecules can collect on the
surface of various materials. This can prevent the build-up
of electrical charges. The reason has to do with the shape
of the water molecule and its own electrical forces.
Thus, static electricity is formed much better when the air
is dry or the humidity is low.
Force field causes attraction
An object that has static electricity charges built up on its
surface has an electrical force field coming from the
surface. This field will mildly attract neutral objects or
those with no charge. The field will strongly attract an
object that has an opposite charge on its surface. From
this we get the expression: "Opposites attract."
If two objects have the same charge, the electrical force
field will cause those objects to push away from each
other or repel.
Law of Electrical Charges
Like charges repel each other and unlike charges attract
each other. Magnets, fly –away hair.
Charged articles will attract opposite charged and neutral
objects, but will only repel like charged objects.
Attraction
Rub a balloon on a wool sweater. The balloon collects
negative electrical charges on its surface and the wool
collects positive charges. You can then stick the balloon to
the wall, which does not have an excess of either charge.
The balloon will also stick to the wool, although the
charges may jump back to the original material in a short
time.
You can also run a comb through your hair to charge the
comb with static electricity. The comb can then be used to
attract neutral pieces of tissue.
Picking up tissue with a comb
Repulsion
Comb your hair on a dry day or after using a hair drier. The
plastic comb collects negative charges from the hair,
causing the hair to have an excess of positive charges.
Since like charges repel, the hair strand will tend to push
away from each other, causing the "fly-away hair" effect.
Why sparks fly
When two objects that have opposite charges get near
each other, the electrical field pulls them together.
What actually happens is that the negatively-charged (-)
electrons are attracted to the atoms in the other material
that have an excess positive (+) charge. Things are much
more stable if all the atoms have an equal number of (+)
and (-) charges.
Strong forces hold electrons
The reason the electrons can't leave their present material
is because of strong molecular forces that keep them
where they are. If there are enough positive (+) charges
attracting them, and the distance is not too great, some of
the electrons will break loose and fly across the gap to the
(+) side.
Once it starts
Once a few electrons start, it heats up the air. (Think about
the heat that is created when you rub your hands
together.) Then more and more jump across the gap,
heating the air even more. This happens very fast, and the
air gets so hot that it glows for a short time. This is a spark.
The same thing happens with lightning, except on a much
larger scale, with higher voltages and current.
Ben Franklin
Ben Franklin proved that lightning was static electricity by
flying a kite in a storm and detecting static electricity by
seeing the hairs on the kite string stand on end and
creating a spark with a metal key. This dangerous
experiment showed that static electricity was being
formed in the clouds by the rain.
In conclusion
Rubbing certain materials together can cause the build-up
of electrical charges on the surfaces. Opposite charges
attract and same charges repel. Either charge will be
attracted to something of neutral charge. Sparks are an
extreme case of electrons being attracted to an object that
is positively-charged.