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SNC1D
PHYSICS
THE CHARACTERISTICS OF ELECTRICITY
L Static Electricity
(P.396,421-423)
Static Electricity
What do lightning and a photocopier have in common? How about that
unexpected “zap” when you reach for a doorknob or your hair mysteriously
standing on end after pulling off a wool hat on a winter day?
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Static Electricity
Objects can become charged when electrons move from one object to
another. The electric charge that builds up on the surface of the object is
called a static charge or static electricity. The charges are “static”
because they remain very nearly fixed in one location on the surface of the
object until they are given a path to escape.
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Static Electricity
For example, the girl below is touching a van de Graff generator – it
generates static electric charge. The student’s hair shows what can
happen when static electricity builds up on someone touching the
generator. Each strand of hair has the same static charge. This makes the
strands of hair repel one another and spread out as far as possible.
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Static Electricity
The accumulation of even larger numbers of
electric charges can lead to some impressive
electrical displays – lightning for example. The
large, bright flashes of lightning are the same
as the small electric sparks you may have seen
when touching a doorknob or taking off a
sweater – they are just different in size.
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Static Electricity
RECALL!
If a neutral object obtains extra electrons, the object becomes negatively
charged. If a neutral object loses electrons, the object becomes positively
charged.
STATIC CHARGE or STATIC ELECTRICITY
electric charge that builds up on the surface of an object
caused by a transfer of electrons
charge remains fixed in place (ie “static”)
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Static Electricity
PRACTICE
1. Why might a plastic rod that contains a large number of electrons not
have a static charge?
because the rod is neutral (i.e. the #e = #p)
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Uses of Static Electricity
Most of the time we think of static electricity as an annoyance. It makes
our hair look messy and can make our clothes stick together. However,
scientists and engineers can use the properties of static charges in many
useful ways in a branch of science called electrostatics. Electrostatics is
the branch of science that deals with static charges and static electricity.
ELECTROSTATICS
the study of static electric charges
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Uses of Static Electricity
PRACTICE
2. Name four applications that use electrostatic principles.
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Uses of Static Electricity
Advertisers use static-cling vinyl film
for brightly coloured removable signs,
decals, and stickers like the one shown.
The windows of many homes, office
buildings, and cars are covered with filters
that screen out sunlight. These screens
use static electricity to cling to the
window.
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Uses of Static Electricity
PRACTICE
3. Explain why it is not a good idea to
try to put up static-cling decals on a
very humid day.
humid air = no static charge (water
molecules in air remove excess
charge)
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Uses of Static Electricity
Electrostatic paint sprayers use
the properties of static charges to
more efficiently paint objects. The
paint is given a charge as it leaves
the nozzle of the sprayer, and the
object to be painted is given the
opposite charge.
The charged
paint particles are attracted to the
object, which minimizes the
amount of wasted paint and
ensures that the object receives an
even coat of paint.
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Uses of Static Electricity
Electrostatic precipitators use
the properties of static charges to
clean the air. Before the gas from a
factory is released it is sent through
pipes that charge the tiny particles
of pollutants, called particulates,
negatively. The gas then moves
through an area that has positively
charged plates which attract the
negative particles and remove them
from the gas. Precipitators use very
little electricity and can remove
about 99% of the particles in
smokestack emissions.
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Uses of Static Electricity
Photocopiers also use the properties of static charges to work.
Photocopiers convert an image captured by a scanner into a laser beam.
This beam is projected onto a drum or belt, creating a negatively charged
pattern (a). The positively charged ink, called toner, is attracted to the
negative charges in the image (b). As negatively charged paper moves
past the drum, the positively charged toner particles are transferred to the
paper (c). The paper than passes through a fuser that melts the toner
particles onto the paper.
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Uses of Static Electricity
USES OF …
static electricity has many practical applications including:
• static-cling vinyl film (removable signs, stickers, …)
• electrostatic sprayer (reduces the amount of wasted paint)
• electrostatic precipitator (cleans the air)
• photocopier
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U Check Your Learning
1. Why does someone’s hair stand on end when they are touching a van
de Graaf generator that is running?
creates the same static charge on each strand of hair – this makes the
strands of hair repel one another and spread out as far as possible
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U Check Your Learning
2. Explain how eliminating static
electricity
would
hinder
the
performance of an electrostatic
paint sprayer.
no static charge = no attraction
(i.e. the paint would just pass by
so you would have to rotate the
object to completely coat it)
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U Check Your Learning
3. How can neutral pollutant
particles be made attractive to
the charged plate in an
electrostatic precipitator?
give the neutral particles a
charge before they enter the
precipitator
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U Check Your Learning
4. Sometimes, finished photocopied paper will stick to you. Explain why.
the paper is still charged from the photocopying process
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U Check Your Learning
TEXTBOOK
P.403 Q.6
P.426 Q.5,6,8,14
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