Static Electricity
Why do objects repel?
 Why do two objects attract?
 Why do they do nothing if you touch them
first?
 Why does the repulsion or attraction only
work if you rub them?
 What does rubbing them do?
 Why does rubbing them with different
materials give different results?
 Which combinations of materials produce
the best results?

Question One:
A cloth is used to rub a thin polythene
strip. This makes the polythene negatively
charged. The same cloth is held near to
the strip. Which two of these statements
are correct?
A.
B.
C.
D.
E.
the strip lost positive electrons when it was rubbed
the strip gained negative electrons when rubbed
the cloth repels the strip
the cloth gains electrons when it rubs the strip
the cloth has become positively charged
Question Two:
The diagram shows two metal balls, P and Q,
hanging from the nylon threads. P is repelled by
and Q is attracted to a negatively charged rod.


A.
B.
C.
D.
E.
Which two statements are true?
P is negatively charged
P is positively charged
P is uncharged
Q is negatively charged
Q is positively charged
Question Three:
A plastic ruler is rubbed on a duster. The
ruler becomes negatively charged.
Which two statements are true?
the duster has also become negatively charged
B. the duster had gained electrons
C. the duster has lost electrons
D. the ruler has gained electrons
E. the ruler has lost electrons
A.
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
These materials lose
electrons
The
Triboelectric
series
These materials gain
electrons
Paper
Aluminium
Silk
Wool
Perspex
Glass
Acetate
Rabbit Fur
Human Hands
Cotton Neutral
Steel
Wood
Amber
Hard Rubber
Polyester
Cling film
Polyethylene
PVC
Silicon
Teflon
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 (!)

Van Der Graaf
Generator
How does it work?
•Rubber belt rubs against plastic
roller
•Charge separation is caused
•Electrons move onto the belt
•Negative charge or electrons
accumulate on the metal dome as
the rubber belt touches the metal
cover
• Negative charges pass onto
the person touching the dome
Roller
─
+
─
+
+
─
─
+
─
+
Rubber
belt
─
─
+
─
+
+
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
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.
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 and SOURCE of free
electrons
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
