Creating Static
Electricity
Electrical Insulators
• Conductivity is the ability of materials to allow
electrons to move freely in them
• Materials that hold onto their electrons and do
not allow them to move easily are called
electrical insulators
• ex) Dry wood, glass, and plastic are all
examples of electrical insulators
• An insulator can hold a static charge because
static charges remain nearly fixed in place.
Electrical Conductors
• An electrical conductor is a solid,
liquid, or gas that allows the movement
of electrons
• ex) silver, aluminum, iron, moist skin,
salt water, water vapor
• A conductor can’t hold a static charge
because it allows the charges to flow
through it
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•
Conductors and
Insulators
Since electrons cannot move through an insulator they
can be very useful to us to protect us from shocks
A simple electric kettle would be very hazardous if the
two wires that supplied electricity to it did not have a
rubber coating over them
Why do we get more shocks
in the winter than in summer?
• This is because in winter the air is far
dryer than in the summer and dry air is
an insulator and therefore does not
take any of the charges our body might
pick up during the day. So when we go
and touch another conductor (a door
handle) ZAP we receive a shock
•
•
Charging by Friction
When two objects made
of different materials rub
together, electrons can
be transferred from one
object to the other
This is because different
atoms (which make up
the objects) have a
different ability to attract
electrons and a different
ability to hold onto their
own electrons.
Electrostatic Series
acetate
glass
wool
fur, hair
calcium, magnesium, lead
silk
aluminum, zinc
cotton
paraffin wax
ebonite
polyethelene (plastic)
carbon, copper, nickel
rubber
sulphur
platinum, gold
Weak hold on electrons
More likely to gain
electrons
Strong hold on electrons
Electrostatic Series
• To determine what charges will form,
compare the location on the table of the two
objects. The object that is higher on the
table will lose electrons and become positive
• ex) when cotton and human hair rub what
charge will form on each object? Cotton is
lower on the list than hair
•
Cotton will hold its electrons better. Hair
will lose its electrons to the cotton and
become positive. Cotton will become
negative.
Electrostatic Series
• Consider the following pairs are rubbed
together. Give charge on each:
• Plastic ________ Silk _______
• Fur __________ Rubber
• glass ____ silk ______
• Vinyl ______ Plastic ______
• Ebonite _________ wool
_____________
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•
•
Charging by Induction
Charging by induction means charging without direct
contact
When a negative charge approaches a neutral object,
the electrons inside the neutral object are repelled. This
causes an induced positive charge on the side closest
to the negative object and an induced negative charge
on the opposite side.
When a positive charge approaches a neutral object,
the electrons inside the neutral object are attracted. This
causes an induced negative charge on the side closest
to the positive object and induced positive charge on the
opposite side.
Charging by
Induction
Induction is used in photocopiers, lightning, dust filters
and electrostatic painting.
Charging by Contact
• Negative charges (or electrons) will always
move from where there are the greatest
number to where there are the fewest
• If there is a big enough difference and the
two objects are close enough together,
this jumping may cause a spark
• When do we see the greatest spark -
when the air is dry or when there is high
humidity ? When the air is dry because dry
air is an insulator
Charging by Contact
•
•
When transferring by
contact, negative charges
move from one object to
the object being touched
Remember! Only the
negative charges move!
Charging by Contact
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Sparks produced by a charge transferred by
contact can be dangerous
Transferring a charge by friction is difficult to
avoid; when charging by contact occurs, one
object is already electrically charged
The other object may or may not be charged,
the important factor is that there is a
DIFFERENCE in the charge on the two objects
Grounding
• The earth is large and absorbs large
numbers of electrons, ground wire is
connected to earth to "dilute" the
charge by carrying it to the earth
Static Electricity can be
Dangerous
• With any phenomena, one of the first things people think of is
whether or not it is dangerous to them. Static electricity can be
dangerous in certain situations.
Lightning
• Lightning during a thunderstorm is very high voltage, high
power static electricity. Getting struck by lightning is extremely
dangerous and kills several people each year. Therefore, you
should be careful about standing in an open field and near
metal poles or trees during a thunderstorm, in order to avoid
getting zapped.
• The record for being struck by lightning and not being killed is
held by a U.S. Forest Ranger. He has been struck by lightning
9 different times!
Dangerous Static
Electricity
Sparks and computers
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•
When you walk across a rug and then touch someone,
you can often cause a spark to fly. This can be irritating,
especially if you touch someone on the nose, but it is
not necessarily dangerous
On the other hand, if you happen to touch a computer
circuit board, the spark — even a very small one — can
severely damage the circuitry. The sudden surge of
electrons can easily fry microchips in the computer.
That is why technicians who work on computers are
very careful to avoid build-up of static electricity
Dangerous Static
Electricity
Explosions
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•
When a gasoline truck fills the underground tanks at a
filling station, they are very careful about any buildup
of static electricity caused by the flowing liquid into the
tank. A static electrical spark could cause an explosion
of the gasoline. Special precautions are made through
the use of grounding cables to prevent any sparks
Another area of concern about static electricity is in
grain elevators and storage bins. When they pour the
wheat or grain into the bin, the air gets filled with a lot
of very fine dust. Any spark caused by static electricity
can cause the dust to ignite and explode.