Static electricity, also known as electrostatics, is a temporary electric charge that builds up on the
surface of an object. It occurs when electrons are transferred from one material to another,
resulting in an imbalance of electrons and a positive or negative charge on each material.
Static electricity is stationary, or "static", meaning it doesn't move. When a static charge moves, it
discharges and the static electricity is neutralized.
How does static electricity occur?
Static electricity can occur through a number of processes. The most common is the triboelectric
effect, which is commonly considered the result of friction. Through this effect, when two objects
are rubbed against each other, electrons from one will "jump" to the other, causing the build up of
an electric charge.
Define charge : It is the product of current and time. SI unit I charge is coulomb (C).
Charge is a scalar quantity. 1 C = 6.24x1018 electrons or protons.
Charge on electron or proton = 1.6x10-19C
The charge e.g; proton or positive ions. Negative charge eg electron or negative ions.
Laws of electrostatic: i, Like charges repel each others. ii, Unlike charges attract each others.
Why an atom is electrically neutrals ?
It consist of same number of protons and electrons both have same magnitude of charge cancel out
completely but opposite sign hence cancel. effect of each others. Neutron is neutral.
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Properties of electric field lines.
i. They originate from the charge and terminate at-ne charge.
ii. They never intersect and cross each other. They are continuous and stretched.
iii. If the gap between field lines are small, it shows strong electric field region.
iv. If the gap between field lines are large, it shows weak electric field region.
v. If the gap between field lines are uniform, it shows uniform electric field region.
Note In Strong electric field region charge experience strong force.
Charging by friction method: Due to rubbing of two objects, heating effect is produced by friction.
The electrons gain energy and may shift from one object to the other.
The object from which electrons are shifted carries positive charge.
The object on which electrons are shifted carries negative charge.
The experimental results of charges by friction are given in the table below:
Note: Charging to friction is suitable for charging insulators.
* Only electrons is responsible for charging bodies because proton and neutrons are bound into the
nucleus so they are not responsible for charging bodies.
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Neutralization
As positive and negative charge combine together, they cancel out the effect of each other. Asa result
spark is produced. This phenomenon is known as neutralization.
Lightning is perhaps the most familiar example of static electricity. Although the exact
process is still debated, the accumulation of static electric charge within a thunderstorm
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cloud is thought to be caused by the triboelectric effect, i.e. friction, between different sizes
of ice and water particles. As these particles are moved higher and lower by wind and
pressure, they rub and bounce against each other, exchanging electrons and gathering
charge. Smaller particles are more easily moved by updrafts, while larger heavier particles
remain more stationary within the cloud. As the different size particles are separated, areas
of positive and negative charge build up. As the charges separate and grow, eventually they
become strong enough to discharge in the form of a lightning bolt, i.e. electrons moving from
areas of negative charge to positive charge. These discharges most often occur within or
between clouds, however, they also occasionally strike the ground.
Uses :
Static electricity has many uses, but it can also be dangerous.
1. Air filters: Static electricity is used in air filters to trap airborne particles.
2. Photocopying: Electrostatic charges are used in everyday situations such as photocopiers
and inkjet printers.
Photocopiers use static electricity to copy paper documents, most commonly
in black and white
An image of the document is projected onto a positively charged copying plate
The plate loses its charge in the light areas and keeps the positive charge in
the dark areas (i.e the text)
A negatively charged black toner powder is applied to the plate and sticks to
the part where there is a positive charge
The toner is then transferred onto a new blank sheet of white paper
The paper is heated to make sure the powder sticks (hence why photocopied
paper feels warm)
The photocopy of the document is now made
Inkjet printers work in a similar way, but instead of the black toner powder, a
small jet of coloured ink is negatively charged and attracted to the correct
place on the page.
3. Paints: Static electricity is used in automotive paints and paint sprays.
4. Dust removal: Static electricity is used in dust removal devices to remove small particles
from smoke.
5. Biological processes: Static electricity is a fundamental part of nerve impulses, which
transmit signals across nerve cells.
6. Insecticide Sprayers
Insecticides are chemicals used to kill pests in order to protect crops
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In order to spray crops effectively whilst using a minimal amount of chemicals, the sprayer
has to deliver the chemicals as a fine mist and cover a large area
To achieve this, the insecticide is given an electrostatic charge (e.g. positive) as it leaves the
sprayer
The droplets of insecticide then repel each other since they are the same charge
This ensures that the spray remains fine and covers a large area
They are also attracted to the negative charges on Earth, so they will fall quickly and are
less likely to be blown away
A similar technique is used in the spray painting of cars.
Dangers of Static Electricity
Static electricity can cause sparking
There are various situations where static electricity can pose a hazard, for example: The risk of
electrocution (e.g from lightning). The risk of a fire or explosion due to a spark close to a
flammable gas or liquid
There are dangers of sparking in everyday situations such as fuelling vehicles such as cars and
planes
Shocks: Static electricity can cause shocks to people.
Skin irritation: Static electricity can cause irritating spots on the skin.
Fire risk: Static electricity can create sparks that could ignite flammable materials.
Electronic damage: Static electricity can damage electrical components in computer chips
and other circuits.
Spacecraft damage: Static electricity can harm a spacecraft's electrical equipment.
Fuelling Vehicles
A build-up of static charge is a potential danger when refuelling aeroplanes. Fuel runs through pipes
at a fast rate. This fuel is very flammable. The friction between the fuel (a liquid insulator) and the
pipe causes the fuel to gain charge. If this charge were to cause a spark, the fuel could ignite and
cause an explosion.
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A bonding line is required to reduce the charge build up when fuelling vehicles. This is prevented by
the fuel tank being connected to the Earth with a copper wire called the bonding line during the
refuelling. The conductor earths the plane by carrying the charge through to the Earth which
removes the risk of any sparks.
How to Prevent Dangerous build up of Electrostatic?
Earthing is used to prevent the dangerous build-up of charge. This is done by connecting the vehicles
to the Earth with a conductor.
To prevent dangerous build-up of static electricity, charged objects can be grounded, which means
connecting them to the earth with a conductor.
Examiner Tips and Tricks:
You could be asked to explain other dangers and uses in your exams
They may ask you to explain the movement of charge in terms of electrons
If asked to explain a danger:
o State what the danger is (electrocution? fire?)
o Explain how the charge can be removed to get rid of the risk i.e earthing (think
about which way the electrons have to move)
If asked to explain a use, think carefully about the forces exerted due to static electricity and
what they will do.
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