Static Electricity

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Static Electricity
When two electrically insulating materials are rubbed together, electrons ­ and nothing else
are rubbed off one material and deposited on the other.
Electrons are negatively charged. The material that lost the electrons is now positively
charged because it has more protons than electrons. The material that gained the electrons
will be negatively charged, because there are now more protons than electrons.
As the diagrams show, the type of material affects which way the electrons are transferred.
The polythene gained electrons from the cloth, but when the Perspex rod was rubbed, it lost
its electrons and became positively charged.
Two objects that have the same electric charge repel each other. Two objects that have
opposite electric charges are attracted to each other. The bigger the distance between the
objects, the weaker the force.
Electric current is the rate of flow of charge. If charge flows through a conductor, there is
a current in it. Electrons carry the charge in solid conductors, such as a metal wire.
Metals can conduct electricity because they contain free, delocalised electrons that can travel
through the metal and carry the charge across.
Insulators cannot conduct electricity because they have no free electrons. All electrons are
held in their atoms.
A conductor can only carry a charge if it is isolated from the ground. It will be discharged if
electrons from to or from the earth. A metal object is earthed by connecting it to the ground.
If a negatively charged conductor is earthed, electrons will from it to the ground until it is no
longer charged. If the conductor is positively charged, electrons will flow from the earth to it.
The bigger the charge on an isolated object, the higher the potential difference between the
object and the earth. If the potential difference becomes high enough, a spark may jump
across the gap.
There are three main uses of electrostatic charge: smoke precipitators, photocopiers and
spray guns.

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Electrostatic smoke precipitators are used in chimneys to attract dust and smoke particles
so they do not get into the air.
1. As the smoke particles go up,
they pass through a negatively
charged grid and become
negatively charged themselves.
2. The grid repels the particles
towards the positively charged
collection plates.
3. The particles stick to the plates
until they are shaken off and
1.…read more

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The greater the charge on the object, the greater the voltage/potential difference is. If the
voltage is too high, a current will flow to the object and might cause a spark.
The problem is overcome by earthing the object. This means joining the object to a large
metal plate in the ground by a conducting wire so any charge just flows to the earth, and the
object's charge is lost.…read more


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