Static Electricity
Benjamin Franklin 1706-1790
Franklin:
-Flew a kite in a thunderstorm to
‘collect’ lightning (not recommended
most who tried to repeat this died)
 Invented Bi focals, Catheters,
Watertight bulkheads, Lightning
Rods and odometers

There are only a few basic laws
of Static Electricity:
Like Charges Repel (--) or (++)
 Unlike Charges attract (- +)
 Charged and uncharged objects attract
 A neutral object has equal numbers of
positive and negative charges
 An object becomes charged when there
is NEGATIVE charge transferred ie
some of the electrons move

How are objects charged?


By Friction
Electrons (-) only are able to travel
Why is this?
-ve electrons
orbiting
around the
nucleus.
Very dense nucleus
consisting of +ve
protons and neutral
neutrons
Note electrons are on the outside of the atoms.
Easier to get at
Electrons which move are known as ‘free electrons’
The positively charged nuclei don’t ‘flow’
So…….
An excess of free electrons means
an object is negatively (-ve) charged
 A lack of free electrons means an
object is positively (+ve) charged
 An electric current is a flow of -ve
charged free electrons ALTHOUGH
conventional current is treated as a
flow of +ve charge (!)

How do we measure static charge?
The GOLD LEAF ELECTROSCOPE
Charged object brought
close to electroscope
Insulator
Charges repelled away from
the charged object, and
repel away from each other
 leaf lifts.
Van Der Graaf Generator
•Belt rubs against lower brush
•electrons added to belt
•work done in moving electrons
creating High voltage
•charge accumulates on dome
So what use is electrostatics?
1.Electrostatic precipitators
5. Cleaner smoke to atmosphere
4. -ve particles are attracted to
+ve plates in chimney.
3. Soot particles touch wire
and become -ve charged.
2. Wires with high negative
charge.
1. Smoke from coal contains
soot particles.
2.Photocopiers
Light causes image
to have +ve charge
-ve charged toner sticks to
-ve charged image
The image is
transferred to paper
The final image is
fixed by heating
3.Electrostatic paint sprayers
Advantages??
Less waste as -ve particles of paint attracted to car
More even coat as each particle repels its neighbour
One last note : The Earth
The Earth acts as a huge source of charge or a
huge sink for charge Excess -ve charge will flow
to the earth from a -ve charged body or up from
the earth to neutralise a +ve charged object
ie The Earth acts as a SINK or SOURCE of free
electrons