ELECTRICITY Part 8 Static electricity and electric fields, uses and dangers
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Doc Brown's school physics revision notes: GCSE
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Electric fields, a simple way to create an
electrostatic energy store
and calculations of current flow in terms of
electrical charge and time
Sub-index for this page
Introduction - making and simply demonstrating
A simple demonstration and explanation of static
Simple demonstrations of
creating and detecting static
electricity on a charged materials
What is an electric field? More on the rules on bringing
More on electric fields - 'maps' of the electric field lines
What happens if the static charge builds up on an
object? - sparks and ionisation
More examples of static electricity, its effects in the
home and anti-static agents
Some uses of static electricity effects - e.g. paint
spraying and particle anti-pollution
More on the nuisance and dangers of static electricity
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Introduction - making and simply demonstrating static electricity, a tale of
FRICTION between materials!!!
This page, I hope, will answer many questions
on static electricity e.g.
What is static electricity? What is an electric field?
How can we produce examples of static
Where in the house or everyday life do you
encounter examples of static electricity?
Can static electricity be dangerous?
Can static electricity be useful?
All matter is made up of atoms, which in turn
are made of a nucleus of positive protons and neutral neutrons and a surrounding
cloud of negative electrons in their specific energy levels ('shells').
matter, most of the time, contains equal numbers of positive and negative
charges so there is net charge of zero and their effects cancel out.
some situations, you can get a build up of negative or positive charge that
cannot flow away like a normal electric current to restore the 'local' zero
balance. This is what we call static electricity.
If a material readily allows the passage
of an electrical current, it is called a conductor.
If a material is poor at conducting an
electrical current, it is referred to as an insulator.
Remember that electrons carry a
negative electrical charge (-).
We've all noticed at some time the
'crackling' or tiny spark effect when taking off or putting on an article of clothing,
particularly with nylon materials, which can also give a similar effect when used as
Well, these are examples of what we call 'static electricity'
and you may even experience a small electric shock as the static electricity is
discharged - through you!
The crackling is the discharge of tiny pockets of
static electricity produced by the friction of clothes or bed clothes
rubbing against each other.
The electric charge flow, the current, is so small
it is highly unlikely to cause you any harm, but you might experience a little
shock - a little prick of pain!
Notice that the materials involved
like nylon, are electrical insulators, not metals, so what is going on?
What is static electricity?
Static electricity is a build up of electric
charge that cannot move or flow as a normal electric current in a conducting
Therefore static electricity usually forms in or on
materials like plastics (polymers) and glass.
Any static charge produced on an electrically insulating material cannot immediately flow away,
- unless a conductor is brought near
the material to discharge the static electricity,
- or it discharges, heating and
ionising air, causing a spark if the potential difference ('voltage')
becomes high enough.
A static electricity spark is an
electrostatic discharge caused by the sudden flow of an electric
current across an air gap. This heats up and ionises the air,
causing light to be emitted. The size of the spark depends on the
distance between the (+ and -) sources of electrical charge and the
potential difference in voltage between them. An extreme example is
lightning, with a p.d. of up to a billion volts (p.d. of 108 V !!!)
The heating causes a rapid
expansion and vibration of the air causing the sound of a
Static charge is produced when two
electrically insulating surfaces are rubbed together.
The static charge is results from the
movement of electrons due to the friction effect when two insulating material
surfaces rub against each other.
an excess of electrons (negative area of static charge) in one material and
of electrons (positive area of static charge) in the other material.
Note that the positive charge does NOT
move, only the negative electrons move in the transfer of charge.
The excess of positive charge created
will be numerically equal to the excess of negative charge created.
The question of which material is positive
and the other negative, from the direction of electron transfer, depends on the chemical constitution of the two
If the electrons can
'leap' back from a negative region to a positive region, the static electricity
is discharged and you see a spark or get a tiny electric shock!
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simple demonstration and explanation of
- creating an
electrostatic energy store
that can do work by picking up bits of paper!
You cannot produce static electricity by
rubbing a metal rod with a cloth because any static electricity formed would
immediately run through the rod into your body or vice versa! However, you can
demonstrate static electricity in a very simple way by rubbing a plastic rod
with a clean dry cloth and getting to pick up little pieces of paper in
which a charge is induced by the electric field of the rod.
You need a bone dry cloth because water,
although a very poor electrical conductor (due to minute
concentrations of H+ and OH- ions), any static
charge would drain away.
I used a polystyrene biro case and a small
cloth used for cleaning my camera lenses (illustrated above).
The duster must be dry so that any static
charge created cannot drain away - water is a very poor conductor, but it
does conduct a little!
Image 1a and Image 1b illustrate the
possibilities of creating static charge by removing electrons with a force of
friction acting between the plastic surface and cloth surface,
but, depending on the two plastic and
cloth materials involved, the electrons can move one way or another between
assumes negative electrons are rubbed off by the cloth making it negative and
the plastic rod becomes positive (deficient in negative charge - electrons).
This tends to happen with acetate plastic rods.
assumes negative electrons are rubbed onto the plastic rod by the cloth making
it negative and the cloth becomes positive (deficient in negative charge -
electrons). This tends to happen with polythene plastic rods.
I don't know which situation applies to this
rod and cloth combination, but that's not the point here. The point is that only
one of two possible static electricity creation situations can result from the rubbing
of two insulating surfaces together and the resulting
electron transfer from the force of friction.
The excess of positive charge created is
numerically equal to the excess of negative charge created, I've marked 8 + and
8 - on each image!
In reality we are dealing with many
electrons, not just the transfer of 8 of them, but it simplifies the
The direction of electron transfer
depends on the nature of the two materials.
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(c) Four simple demonstration
methods of detecting static electricity on a charged plastic rod
Getting the rod to pick up tiny bits of
I used a few bits of very fibrous kitchen role (a large surface area
which helps) and
a biro case as the plastic rod.
It works even better with a more solid
rod of poly(ethene) ('polythene') or Perspex.
Image 2a: The plastic rod (biro) is charged
by rubbing in vigorously with a clean dry cloth to charge it up with static
Image 2b: If the charged rod is carefully
held close to some small bits of uncharged paper, they are picked up and sometimes as a
The charge on the rod induces the opposite
charge on a bit of paper by pulling or pushing electrons on the paper surface.
opposite charges then attract each other, so the bits of paper are attracted to
The effect can be transmitted to a second bit of paper giving a little
paper chain held together by static charges.
The plastic rod - paper chain will
hold together because both materials are electrical insulators and the
electrical charge is slow to drain away.
You need to imagine the following:
either: plastic - ... + paper bit - ...
+ paper bit -
the negative plastic rod repels the
electrons inducing a positive charge on the paper surface
or: plastic + ... - paper bit
+ ... -
paper bit +, where the positive plastic rod attracts the electrons on the
where the dotted line ... represents
the electric field attractive force.
This is actually a simple test to
show the plastic rod was charged up with static electricity.
Suspended charged rods
You charge plastic rods of cellulose
acetate, Perspex and polythene by rubbing them with a dry dusting cloth.
Polythene becomes negatively charged -
gains electrons, so the duster becomes positively charged - lost electrons.
Perspex and cellulose acetate becomes
positively charged - the plastic loses electrons, so the duster becomes
negatively charged - gained electrons.
You can then suspend the rods, finely
balanced with a fine thread and are perform simple attraction and repulsion
e.g. you should be able to
two rods of the same plastic
repel - like charges repel,
polythene rod (-) should
attract either a Perspex rod (+) or an acetate rod (+), unlike
a Perspex rod should repel a
cellulose acetate rod.
Think of the circles as a
cross section of the plastic rod and the + and - signs as the
static charge on the surface,
from electron loss and
(-) from electron gain.
Another simple demonstration of an electric field effect
- a kitchen sink experiment!
A simple 'kitchen sink' experiment that
clearly shows the effect of an electric field.
Image 3a: You get the thinnest continuous
stream of water descending from a tap.
Image 3b: You then charge up the plastic rod
(biro) and carefully hold it quite close to the water stream, BUT not touching
(this discharges the static charge into the water). The plastic rod is to the
right of the stream. The electric field around the plastic rod attracts the
water molecules attracting the water stream towards the plastic rod.
Technical points of explanation (its more
A level chemistry, but no matter!):
Water is an neutral covalent molecule
However, water is known as a 'polar molecule' and one end
is naturally slightly positive and the other end slightly negative (electrically
It doesn't matter what the sign of
the charge is on the plastic rod.
If the rod is -ve it attracts the +ve
end of the water molecules, if the rod is +ve it attracts the -ve end of
the water molecule.
Therefore whatever the rod's static
charge sign, the stream of water molecules is attracted towards the
statically charged rod.
Again, this is a simple test to
show that the plastic rod is charged and it doesn't matter whether it
holds a positive or negative charge.
The deflection shows up better as the shadow on the
The gold leaf electroscope
How a gold leaf electroscope works
The gold leaf electroscope consists of a zinc
plate mounted in an insulated wooden box with windows (so you see what
Attached to the stem of the zinc plate is a
thin sheet of gold (gold leaf).
Both metals should not be carrying a static
charge - you ensure any charge has been discharged by touching the top with any
conding rod of metal.
An insulating plastic rod is charged up by
rubbing with a dry duster cloth.
Let us assume it carries an excess of
electrons i.e. the plastic rod carries a negative static charge.
If the plastic rod is touched onto the zinc
plate, you get a charge transfer and some electrons will flow down into the
conducting zinc plate AND the equally conducting gold leaf.
Therefore both the zinc rod and the gold leaf
have the same negative charge and will repel each other (- -), so the
gold leaf moves apart from the zinc rod and curls up.
If you then touch the zinc plate with any
other metal rod, the electrons will flow into it and the static electricity is
then discharged through your hand and the gold leaf falls back against the zinc
rod. This might not work if you are wearing rubber gloves!
Repeat experiment with another plastic rod of
If the plastic rod is positively charged
with static electricity, electrons will drain from both
metal strips making them both positive, repulsion
should take place i.e. the gold leaf will be repelled from
the zinc surface.
You can also touch the 'uncharged' zinc
plate with a positively charged insulator and this time the electrons will
flow onto it from the plate making both metals positive. Therefore the gold
leaf will rise due to the like charge repulsion (+ +). Look at the diagram
and just imagine swapping the -ve signs for positive signs, its the same
effect in the end.
Note: Because the zinc and gold leaf are
themselves insulated from the 'earth', in this case, you can have an
electrically conducting material that will hold a static electric charge. In an
exam, never say a metal plate can never hold a static charge!
(5) The spectacular Van de Graaff
A Van de Graaff machine involves an
insulating belt continuously rubbing over copper contact brushes which are
connected to a steel dome.
The friction causes static charge to
build up in the belt and metal contacts.
The steel dome, despite being a good
electrical conductor, is insulated by the surrounding air (up to a
Therefore there is no complete circuit
and static electricity can build up.
The static charge gradually builds up as
the machine runs and can be spectacularly released if another conducting
metal sphere is brought near the steel dome,
BUT, if you hold the sphere without
rubber gloves, the static electricity discharges through you with a
spark that jumps across!
BUT, don't worry, although the p.d.
voltage is high, the current is very small and harmless.
The potential difference between the
sphere and dome is so great that the static charge discharges, jumping
through the air to the sphere - the p.d. is so great the hair is heated up
and ionises at high temperature, causing a discharge of light energy and
sound energy too.
However, before switching on the Van
de Graaff generator, you place your hands on the sphere and then switch
the machine on.
You need to be insulated by
standing on a thick plastic or rubber mat - otherwise the charge
The resulting static charge
builds up in your body, including your hair.
The hairs on your head have the
same positive or negative static charge and so they repel,
giving you an impressive 'spaced out' and startling hair style !!!
need diagram and
See later section for full
explanation of why you see a spark.
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What is an electric field?
What are the rules on bringing charges together? (already covered, just reminders here)
An electric field is created around any
particle or object that has an overall positive or negative electric charge.
Any pocket of static charge on an object,
when brought near another object that is also carrying a static electrical charge then one
of two things can happen.
When an electrically charged object is placed in an electric
field e.g. from another charged object, it will experience a force due to the
interaction of two electric fields.
The magnitude and direction of this force is determined by
three factors, which are all to do with the strength of the electric field.
Also note that both charged objects experience a force
e.g. both the objects Q and q move apart or come closer together.
1. Direction of the force
If the static charges are alike, two
positive or two negative charges, then a force of repulsion occurs
between the objects, pushing them apart.
This is called electrostatic repulsion,
a non-contact force.
If the static charges are different, a
positive and a negative charge, then a force of attraction occurs between
the objects, attracting them together.
This is called electrostatic
attraction, a non-contact force.
This force acts due to the presence of an
electric field around each object which do NOT have to be in contact with each
You can demonstrate rule 1. by suspending
two different plastic rods of different static charges and bring them
towards each other e.g. two of the same charge brought near each other OR
two plastic rods of opposite charge.
Rule 2. The size of the charge
For oppositely charged objects, the greater the two electrical charges e.g.
Q+ and q-, the greater the force of attraction between the charged objects. The
strength of the electric field is increased by increase in the magnitude of
If the two charges are of the same sign
(+ + or - -) then the greater the magnitude of the charges, the greater the
force of repulsion pushing them away from each other.
Rule 3. The distance between two charged
For oppositely charged objects (+ve and
-ve), the smaller the distance between the two
static charges, Q+ and q-, the greater the force of attraction between the charged objects.
The strength of the electric field is increased by decreasing the distance
between the charges.
If the two charges are of the same sign
(+ + or - -) then the closer they are, the greater the force of repulsion
pushing them away from each other.
(at higher level i.e. A level, the force of
attraction is proportional to charge Q+ x charge q- / d2)
Electric charge is measured in coulomb
units, denoted by C.
See separate page for
of the charge passing through a point in a circuit Q = It
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More on electric fields - 'maps' of the electric field lines
Can we map out the field lines of a static
electric field (as with magnets!)?
An electrical field is created around any
electrically charged object.
The electric field of an object is the
region that will experience a force if a second charged object is moved into it.
The nearer you are to a charged object AND
the bigger its charge, the stronger
the electric field effect is.
The orientation of field lines around a charged object
The diagram above shows the direction of the
field lines in an electric field emanating ('spreading out') from two isolated
spherical objects, one positively charged Q, and one negatively charged
The lines of the electric force field go
from positive to negative and at right angles to the surface of the
The closer together the field lines
are, the stronger the electric field - you can tell from the diagram the
field is strongest the closer to the centre of charge you get.
The diagram above forms the basis for showing
the electrical field around an object for an isolated positively charge object
and an isolated negatively charged object.
By convention the field lines run
from positive to negative as indicated by the added arrowheads.
Electrostatic force field diagrams when
The above diagrams show the maps of field
lines for electrically charged objects when you get:
Note the electrostatic charge convention that
the field direction is from positive to negative.
ATTRACTION: when two oppositely
charged objects approach each other (+ve and -ve)
Here the field lines join up between
the two charged particles.
If the charged objects are free to
move towards each other, the field lines will strengthen, become closer together, as the
attractive force increases.
REPULSION: when two objects of the
same charge approach each other (two +ve or two -ve).
Here the field lines do not join up,
but are pushed away from each other.
If the charged objects are free to
move apart, the field lines will weaken as they become further apart, and the attractive
The closer the field lines are together
the stronger the electrical field effect.
This happens as you get closer to any
charged object OR if the charge is increased, which also increases the
electric field strength.
You can see this as the field lines get
closer to the source of the static charge.
See also the three rules in the previous
Note: The greater the potential
difference between the charges, and the closer the charge fields are, the
more likely you are to see the spontaneous discharge of the electrical
energy and a visible spark.
Parallel charged plates
The electric field between parallel plates
The electric field between two oppositely
charged parallel plates is quite uniform with all the field lines parallel to
each other and all exactly at right angles to the surfaces of the plates.
Therefore the strength of the electric field is the same at any point between
the plates and will only differ at the ends of the plates where the field lines
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What happens if the static charge builds up on an object? - sparks and
The full explanation of
sparking (Van de Graaff generator, hair and comb or 'lightning' - its
all the same!)
You cannot get a visible spark in a
vacuum, because there are no particles to excite to the point of emitting
Ignoring the uncharged neutrons, atoms
contain positive nuclear protons and surrounding negative electrons.
At room temperature, unless a chemical
reaction is taking place, everything is electrically balanced, and atoms and
molecules are stable, including those of air.
Under these circumstances,
air is an
electrical insulator BUT ....
However, if there is a powerful
electrical field (more
on fields in previous section), the very high potential
difference causes the atoms and molecules in air to
ionise and break up into
positive ions and negative electrons.
The electric field is so powerful it
removes an outer electron from the atom or molecule - the process
The formation of ions increases the
electrical conductivity of air, so the discharge - flow of current,
The charged particles come together
discharging the electrical energy, heating the air and exciting the air
particles so much they emit visible light.
The electrons of the excited atoms or
molecules fall back down to their original energy levels emitting
visible photons of light in the process - so we see a spark of light.
You cannot see a visible spark in a
vacuum because there are no atoms or molecules to be excited and ionised to
the extent that they will emit energy as visible light photons.
Charge movement or not?
Under normal circumstance the potential
difference between the earth and any object is 0V (p.d. of zero volts). However,
If electric charge increases on an object the p.d. between the object and the
earth rises above 0V. If the potential difference is great enough,
electrons can leap across the gap between the charged object and the earth.
The electrons, effectively an electrical
current, can jump the gap to any conductor in the vicinity that is earthed (in
contact with the ground), though for small p.d. voltages the gap must be small.
e.g. (i) If static charge has built up on
an article of clothing, as you remove it the electrons can move through your
body to earth via your hands and you feel a 'crackling' shock and maybe see
some sparks of light!
(ii) As a car is moving along the
friction between the car body and the air can cause the build up of static
charge because the car body is insulated from the earth by the rubber tyres.
As you get out of the car and touch the metal body the static electricity
can be discharged through your body to earth and you experience a small
(iii) The Van de Graaff generator
experiments have already been described.
In the case of lightning you are dealing with
a massive build up of static charge in clouds, and the potential difference
between the earth and atmosphere is very large. Consequently lightning strikes
('huge sparks') occur across some pretty big gaps between the earth and clouds
with spectacular visual results!
The static charge in clouds is caused by
ice particles bumping against each other and becoming charged by friction.
Lighter positive ice particles accumulate at the top of the cloud and heaver
negative ice particles collect lower down.
When the number of charged
particles increases, at some point, you get a massive discharge of
electricity as the oppositely charged particles come together to give a
giant spark - a flash of lightning.
Sometimes the clouds of negative particles induce a positive charge on the
ground and then discharge takes place from cloud (-ve) to ground (+ve), and
this is a lightning strike (diagram on the right).
If a negatively charged thunder cloud
passes over, it induces a positive charge on the nearest object on the
ground e.g. a church spire lightning conductor, and, on the bottom end
of the lightning conductor, a negative charge on the copper earth plate.
The electrons travelling down the
copper lightning conductor and rapidly dissipated safely into the
Unfortunately this positive charge
builds up on any tall objects nearer the cloud's charge e.g. like tall buildings or trees,
and that's why in a thunderstorm you should not take refuge under a tall
tree - its nearer than you to the charge cloud!
Being inside a car does protect you because the electrical discharge
can run through the car body to earth, but avoid touching the car body until
the event has passed!
So, sparks occur when there is a big enough
potential difference between a statically electrically charged object and any
object that is connected to earth (an 'earthed object').
This high p.d. creates
a strong electric field between the two objects ('charged' and 'earthed').
In industry, and the home to, you can use of insulating mats
shoes with insulating soles if there is a danger of an electric discharge
through your body.
If the electric field effect is strong
enough, that is if the potential difference is great enough, electrons can be
remove from particles in the air, a process called ionisation and
positive particles are formed (+ve ions).
Air is a good electrical
insulator but the presence of these ions makes it a better conductor so an
electrical current can flow.
This can be sometimes be seen as a spark because
some of the electrical energy is converted to heat and light energy.
I've written more about these examples and
how to counter the effects of static electricity in the final section of the page.
If any object can be connected to the
'earth', by e.g. a conductor such as a copper wire or strip, then any build up
of static electricity can be safely discharged.
This is called earthing
You can get an electrostatic shock if you
are electrically 'charged' yourself and you touch something that is earthed,
so the static electricity runs through you.
Similarly if you yourself are
earthed and you touch something that is charged, you can also get an
That's why household circuits and electrical appliances
should be earthed for your safety and protection.
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(g) More examples of
static electricity and its effects in the home
As already mentioned, whenever certain
clothes rub up against each other, the friction between the surfaces can
generate static electricity which can then discharge causing tiny sparks or tiny
This can cause clothing to stick to you as 'prickling effects' from the
tiny electrical discharges.
Polishing surfaces to make them look clean
and shiny also generates static charge on the surface and attracts fine dust
particles e.g. on table tops.
High voltage equipment can create static
charge e.g. dust collects on TV and computer screens.
You can rub a balloon on your sweater to give the rubber
surface a static charge, it can the induce an opposite charge on the surface of
a ceiling and so it can stick there!
Note that before the rubbing
together, both objects are electrically neutral, but after rubbing the
two together ....
if the balloon loses electrons to the
sweater, the balloon carries a positive charge, therefore the sweater
will induce a negative static charge on the ceiling surface by attracting
electrons, and the balloon sticks to the ceiling.
but, usually, the rubber balloon
carries a negative charge, gaining electrons from the sweater rubbing.
The balloon will therefore induce a positive
static charge on the ceiling surface by repelling electrons.
So attraction of opposite charges
attract, and the balloon sticks to the ceiling!
This is known as
attraction by induction,
and will do the same to your hair, which is attracted to the balloon!
When you run a comb through your hair
electrons can be transferred to the comb giving it a negative static charge.
Both the comb and hairs acquire a
can then pick up bits of paper (see earlier section). Your hairs might also be
attracted to the comb instead of staying in place!
When you walk on a vinyl floor or one covered
with a nylon carpet you 'charge up' because of friction between you and the
carpet, which can result in getting an electrostatic shock by touching a
conducting material such as a metal door handle, water tap or even another
e.g. If you touch a water pipe (automatically
earthed) after walking on a floor covered with an insulating material like
synthetic carpet or vinyl tiles you may experience a small electric shock from
the build up of static electricity on your clothing.
Many electrically insulating surfaces
like plastic or wood, when polished, become charged when rubbed in dusting.
Therefore, polished surfaces readily
attract the dust back again!
Some dusting brushes are designed to
be charged, and induce a charge in dust particles to attract and collect
Anti-static spray coatings are made from
a conducting polymer dissolved in a solvent made from deionized water and
When the solvent evaporates, it
leaves behind a very thin conducting skin on the surface of the object
that drains any static charge away and prevents further static build-up.
You can also get a cloth that does
the same job.
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Some uses of static electricity effects - e.g. paint spraying
and particle anti-pollution
(a) Electrostatic sprayers are used in industry
to give a thin even coating of whatever is needed to coat the surface e.g. using
an electrostatic spray gun to paint the body of a car or any other object
that can be given a static charge.
An electrostatic paint sprayer (spray gun)
gives the tiny droplets of paint a negative static charge. The object to be
painted/coated is given a positive static charge.
As you operate the spray gun, each tiny paint drop is
repelled by any other (like charges repel) giving a fine and even dispersion of
paint in the spray. When the spray comes near the car body the negative droplets
are attracted to the positive surface of the car body and the charges
neutralised as a fine and even layer of paint forms on the surface.
The positive electric field of the
bicycle frame interacts with the electric field of the paint droplets.
Electric field lines and spraying
This enables the coating to be highly controlled and the spray easily surrounds any shape so you
shadow regions of no or little paint and neither do you get excess paint
thickness either, so very little paint is wasted.
The same principle applies to insecticide
sprayers which work in a similar way to protect crops from pests.
However you can't give the plants a static
charge directly! and for environmental reasons, you want to minimise the amount
of insecticide used - minimising harmful pollution side-effects to other animals or
To spray the crops, you use a low-flying
aircraft fitted with a spray gun connected to a reservoir tank of the
Instead the droplet-particles of the insecticide are given a
static charge which makes the like-charged particles repel and spread out more
evenly compared to a conventional multi-nozzle spray system.
Then, on spraying onto the plant crops,
the insecticide droplets induce the opposite
charge on the plant leaves (induction).
So the insecticide is attracted
over the surface of the plant and coats in a much more even manner.
Its the same
principle as a rubbed balloon sticking to the ceiling or spraying the car with
paint described in (a)!
(b) Trapping pollution particles in
Static electricity in the form of charged
plates across which a large negative potential difference (50,000 V) is applied can be used to
minimise the dust and smoke particles in discharges from factory chimneys.
These consist of fine solid particles
- some potentially harmful
The waste gases pass through a negatively
charged metal mesh. This large static charge induces a negative charge on the
smoke particles or dust. Further up the chimney the negative dust/smoke particle are attracted to
the oppositely charged positive plates (again a very high, but positive voltage) and removed from the air
before the smoke leaves the chimney. The statically attracted particles collect
in the L shaped trays below the positive plates.
Every so often the collection plates have to
be shaken to remove the collected particles of dust and soot and the trays
process is called electrostatic precipitation and the apparatus is called
the electrostatic precipitator (electrostatic smoke precipitator, to be
electric field removing fine particles from smoke
Photocopiers and printers use static electricity to
copy images onto a statically charged plate before printing them.
Laser printers use static electricity to
print out documents.
Inside the printer casing is an image
drum that is initially given an overall positive charge.
A laser is shone onto the drum producing
a negative image on parts of the drum corresponding to the original document
The toner, the powdered ink in the
printer cartridge, is given a positive charge.
Therefore the ink powder is attracted to,
and sticks to, the negative areas of the image drum.
Then negatively charged printer paper is
rolled across the image drum.
Because the negative charge on the paper
is stronger than on the image drum, the positively charged ink powder is
transferred from the image drum to the paper,
The paper is then heated to fuse the ink
powder to the paper, hence visually reproducing the contents of the original
document or file.
TOP OF PAGE
on the nuisance and dangers of static electricity
As already mentioned, any object connected to
the 'earth' by a conductor (earthing charged objects) then any
static electricity can be safely discharged.
The most dramatic example is a
As previously described, lightning is
a very powerful and potentially dangerously destructive discharge of static
electricity. Apart from their obvious danger to human beings, lightning strikes
can seriously damage buildings, especially tall ones, were the highest point is
nearest to the source of static charge.
For example church steeples have a strip
of copper from the peak of the spire running right down to be embedded in the
ground - earthed. When the lightning strikes, the discharged static electricity
heads for the most electrically conductive material, the copper strip, rather
than the insulating stone, and runs safely into the ground. Without the
lightning conductor the build up of energy at the top of the building is so
great it cause physical damage to stonework and set fire to roof timbers.
As a car,
or any other road vehicle, is moving fast through air, static charge can build
up on the body of the car through friction.
To avoid any irritating or dangerous
consequences, you can have a metal contact e.g. a copper strip in a plastic
sheath (brown strip on the diagram above) that electrically connects the metal
body of the car to the 'earth'.
This allows any static charge formed to drain
If the car is positive the charge is 'neutralised' by electrons flowing
from the road (the 'earth') or if the car is negative, then the negative static
charge of electrons can be safely discharged to the road through the copper
Static charge is easily formed by a plastic
surface rubbing against another surface e.g. plastic vinyl floor tiles, nylon
comb through your hair, synthetic fibres in clothing, etc.
To minimise these
effects plastic additives called antistatic agents have been developed to
minimise the build up of static electricity.
To these plastic products special
molecules called anti-static agents are added to the polymer mixture from the
object/material is made.
These antistatic agents make the surface of the polymer
slightly conductive and enough to allow any static charge formed to be
discharged and so dispersed to give no noticeable effect.
You can uses
anti-static sprays to coat surfaces to increase the surface conductivity to reduce the problems of static
electricity - you can treat car seats in this way too.
Refuelling and filler pipes:
vehicle fuel tanks at the petrol station, fuel tankers themselves, aircraft fuel
tanks etc. are being filled the friction of the flowing fuel against the pipe
hosing can create static charge.
Therefore, fuel delivery systems must be
(most importantly) earthed and anti-static liquid agents may be added to the
fuel to increase its electrical conductivity to drain away any potentially
The hose piping itself can be treated
with an anti-static agent to avoid the build up of static charge, that,
if discharged, may create a spark potentially causing a fire or explosion in an
air - petrol vapour mixture.
Static electricity can build up on the body
of an aircraft as it flies through the air at great speed, so a great friction
effect cannot be avoided.
Therefore the plane does become charged and this
static charge can interfere with communication systems.
Modern aircraft are fitted with
static dischargers, which moderate the amount of static charge that
builds up on the aircraft.
In a factory, machinery operators using high
voltage machines, stand on insulating mats or wear shoes with insulating soles
to stop any charge flowing through them to the Earth.
Protection against a static electricity
discharge must be in place where equipment is used in atmospheres where explosions could
occur eg inflammable gases or vapours or with high concentrations of oxygen
Most of the situations I've described will be
familiar to most people, but how many of you realise the dangers of very fine
combustible powders moving in the air!
In the past there have been coal dust
(coal mine) and flour (flour mill) explosions due to the friction between moving
fine dust particles and the surrounding air.
The fine powder particles have such
a large surface area for friction to take place that sufficient static charge can build up to create a
The 'surface area rule' in chemistry kicks in (rates
of reaction factor) and rapid combustion ensues from the heat
generated, causing the powder and oxygen in the air to explode !!!
TOP OF PAGE
key words key phrases: Appreciate that electrostatics plays an important part in our lives. You investigated some of the ideas of electrostatics and look at the problems
caused. Suggested practical and research activities to
revise from Carry out
experiments to compare how effective different types of duster are Investigate the effect of charged insulators on small uncharged objects. Carry out experiments to demonstrate the forces between charges. Carry out experiments to create static charges, and investigate
the effects that result. Recognise that when some materials are
rubbed they attract other objects: certain
types of dusting brushes become charged and attract dust as they pass over
that insulating materials can become charged when rubbed with another
insulating material. Be able to state that there are two kinds of
electric charge, positive and negative. Be able to describe how you can get an electrostatic shock
from charged objects eg synthetic clothing. Be able to describe how you can get an
electrostatic shock if you become charged and then become earthed eg
touching water pipes after walking on a floor covered with an insulating material
like synthetic carpet. Know that like charges repel and unlike charges attract. Understand that electrostatic phenomena are caused by the transfer of
electrons, which have a negative charge. Be able to
describe static electricity in
terms of the movement of electrons: a positive charge due to lack of
electrons a negative charge due to an excess of electrons. Know that
atoms or molecules that have become charged are called ions. Be able to explain how static
electricity can be dangerous when: in atmospheres where explosions could
occur eg inflammable gases or vapours or with high concentrations of oxygen in situations where large quantities of charge could flow through the body to earth. Be able to explain how static electricity can be a nuisance: dirt and dust attracted to insulators (plastic containers, TV monitors etc) causing clothing to “cling”. Be able to
explain how the chance of receiving an electric
shock can be reduced by: correct earthing use of insulating mats using
shoes with insulating soles bonding fuel tanker to aircraft. Be able to
anti-static sprays, liquids and cloths help reduce the problems of static
Usefulness of electricity, safety, energy transfer, cost & power calculations, P = IV = I2R,
E = Pt, E=IVt
Electrical circuits and how to draw them, circuit symbols, parallel
circuits, series circuits explained
3. Ohm's Law, experimental investigations of
resistance, I-V graphs, calculations V = IR, Q = It, E = QV
4. Circuit devices and how are they used? (e.g.
thermistor and LDR), relevant graphs gcse physics revision
5. More on series and parallel circuits,
circuit diagrams, measurements and calculations
gcse physics revision
6. The 'National Grid' power supply, environmental
issues, use of transformers
physics revision notes
Comparison of methods of generating electricity
physics revision notes (energy 6)
8. Static electricity and electric fields, uses
and dangers of static electricity gcse
physics revision notes
- magnetic materials - temporary (induced) and permanent magnets - uses gcse
Electromagnetism, solenoid coils, uses of electromagnets gcse
physics revision notes
11. Motor effect of an electric current,
electric motor, loudspeaker, Fleming's left-hand rule, F = BIL gcse physics
Generator effect, applications e.g. generators
generating electricity and microphone
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