Static
Electricity
Static Electricity
Static electricity is a build-up of electric charge that does not
move (it stays in place). Static means stationary or still.
Effects of Static Electricity
The Explanation (Theory) for Static Electricity
All substances are
composed of
atoms. Atoms
have a small but
heavy positive
center (the
nucleus). Around
the nucleus are
light, moving,
negative electrons.
A Review of the Charge Laws
Like charges repel
each other.
Opposite charges
attract each other.
Outer Electrons Can Escape
Electrons in the outer shells of atoms are not held as strongly
as inner electrons. Outer shell electrons can be pulled away
from an atom by friction, when one object rubs another.
The Explanation (Theory) for Static Electricity
Normal substances are neutral because their atoms have the
same number of positive charges (protons) as negative
charges (electrons).
When Electrons Transfer, Objects Become Charged
When electrons move into a neutral object, it becomes
negatively charged.
When electrons move out of a neutral object, the object
becomes positively charged.
Grounding an Object
Grounding is usually used to remove the charge build-up on
an object but it can also be used to charge an object (This
will be discussed later.). When an object is grounded, it is
connected by means of a conductor (metal) to some other
much larger object (often the earth or ground). Electrons are
free to move into or out of the ground into the object until it
Grounding an Object
Grounding removes a charge as long as the grounding object
is larger than the discharging object. For example, a tiny pith
ball is neutralized when a person touches it (the person’s
body
is huge compared to
the tiny pith ball.)
Insulators
Substances that hold a static charge when rubbed are called
insulators. Dry air, glass, plastic, cloths, wood, paper and
rubber are insulators. Insulators hold electrons in place and
do not let them wander or move about. Grounding a charged
insulator (connecting it to a large object) will NOT remove the
charge.
Conductors
Conductors will NOT hold a static charge when rubbed.
Metals and graphite (pencil lead) are good conductors.
Conductors allow their electrons to roam freely through
them. Conductors will hold a static charge if they are
insulated. Grounding a charged, insulated conductor will
remove the conductor’s charge.
The Effect of Charged Objects on Conductors
Charged objects induce (cause) charges to separate in
neutral conductors.
The Explanation (Theory) for Static Electricity
In solid materials, the positive centers are fixed in place, just
vibrating. This means that the positive charges (protons) do
not move. The negative charges (electrons) are light and are
able to move from place to place. (phet demos)
The Explanation (Theory) for Static Electricity
Different substances have different attractions for electrons.
For example, the atoms in plastics tend to attract electrons
more strongly while the atoms in wool tend to have a weaker
attraction for electrons.
The Explanation (Theory) for Static Electricity
When objects are rubbed together, electrons move towards
the substance which has the greater attraction for electrons.
This leaves one object negative and the other object equally
positive.
The
Triboelectric
Series
The Triboelectric
Series is a chart
that shows the
charge that
objects will get
when rubbed
together. When
wool and plastic
(PVC) are
rubbed, the wool
becomes positive
and the plastic
becomes
negative.
The Electroscope
An electroscope is a device used to detect the kind and
amount of electric charge on a charged object.
Bringing a Charged Object Near an Electroscope
The leaves of a neutral electroscope separate when a
charged object approaches the electroscope. This happens
because the charged object repels electrons into the leaves,
making them the same charge which causes them to repel
away from each other.
Charging an Electroscope by Conduction
When a neutral electroscope is touched by a charged object,
it becomes charged with the same charge as the charged
object that touched it. This is called charging by conduction
or charging by contact.
Charging by Conduction With Negative Object
When a neutral electroscope is touched by a negativelycharged object, some electrons move from the negative rod
into the electroscope so that it gets the same charge as the
object that touched it.
Charging by Induction
An electroscope is charged by induction when a charged
object is brought close to it but DOES NOT touch it and then
the electroscope is grounded (connected to a large
conductor or the earth via pipes/wires).
Charging by Induction
When an electroscope is charged by induction, it gets a
charge that is opposite the charge on the charged object that
is brought close to the electroscope.
Neutral Objects Always Attract to Charged Objects
Charged objects brought near to neutral objects cause the
neutral objects to separate their charges so that the opposite
charge faces the charged object.
Neutral Objects Always Attract to Charged Objects
Since a neutral object separates its charges with the opposite
charge facing the charged object, it will always attract to the
charged object since it takes on the opposite charge.
Using Static Electricity: A Photocopier
A photocopier uses static electricity to make an invisible
electrostatic image on a paper and attract oppositely-charged
powder to this paper, using heat to bond the powder to the
paper.
Using Static Electricity: A Photocopier
A photocopier uses static electricity to make an invisible
electrostatic image on a paper and attract oppositely-charged
powder to this paper, using heat to bond the powder to the
paper.
Using Static Electricity: Removing Pollution
Electrostatic precipitators help to remove pollution from air
(in factory stacks or in homes – dust removal).
Using Static Electricity: Efficient Painting
Paint is given one charge and the object to be painted is
given an opposite charge. The paint attracts to the object.
Controlling Static Electricity: Preventing Sparks
Many vehicles have ground strips to prevent a build-up of
static charge (could cause sparks that could ignite gasoline
fumes). Tanker trucks typically have grounds in their hoses
to stop the formation of sparks.
End of Presentation