CHAPTER ONE: STATIC
ELECTRICITY
1.10 Concept of static electricity
Static electricity is the electricity resulting
from the accumulation of stationary electric
charges on a material that does not conduct
electricity.
Note that: Electrostatic charges are
stationary in nature. The rubbing only can
transfer the charges.
EFFECT OF STATIC ELECTRICITY
1. When a dry cloth is used to clean a glass
window, tiny pieces of cloth and dust
adhere to the glass.
Because, the friction between the cloth
and the glass creates static charges,
which then attracts dust particles due to
their opposite electrical charges.
2. When you rub feet on a carpet and then
touch a metallic object, you experience a
slight electrical shock
Because, your body accumulates static
charges. When you touch a metal
surface, which is a good conductor, the
charge can discharge to the metal,
resulting in electric shock.
3. An air craft in flight accumulates
charges on its outer surface because it
rubs against the air.
If a person touches the outer surface of
the air craft on landing after a long flight
may experience a slight electric shock.
Because, the accumulated charges on the
plane will be transferred to the body
resulting in electric shock.
4. Nylon clothes crackles as you undress.
This is due to accumulation of excess
charges which creates electric force
between the nylon cloth and the human
body.
5. The TV screen dust after a while.
Because there is accumulation of static
charges, the dust particles are attracted by
the charged TV screen.
APPLICATION OF STATIC CHARGES
1. Petrol road tankers usually have a
chain touching the ground: The chain
is for earthing. It transfers excess
charges to the ground.
2. Air filters and dust removers: They use
difference in charge between materials
to trap airborne particles.
3. Inkjet printers: They use static
electricity to bind ink to paper.
Example 01
After walking across a carpeted floor, you
sometimes get a mild electric shock when
you touch a metal door knob. Explain how
this happens?
Answer
While walking on a carpet electric charges
accumulate on your body. The door knob
also has excess opposite charges. This
results in a mild electric shock.
Example 02
Explain why nylon clothes crackle as you
undress.
Answer
This is due to accumulation of excess
charges which creates electric force between
the nylon cloth and the human body.
Example 03
Explain why petrol road tankers usually
have a length of metal chain hanging down
touching the ground.
Answer
The chain is for earthing. It transfers the
excess charge to the ground.
Example 04
Why some clothes tend to cling onto the
body by a person.
Answer
Because the friction between the clothes and
the body cause static charges to accumulate
Example 05
Why do TV screens become dusty after a
while? Discuss.
Answer
The dust particles are attracted by the
charged TV screen
ELECTROSTATIC
Electrostatic is the study of stationary
electric charges
Electrostatic force is the force caused by
the interaction electric charges that are at
rest.
The electrostatic force can be repulsive or
attractive.
Example 01:
After charging plastic rods by rubbing them
with a piece of fur, the rods repel each other.
Then the force is repulsive
Example 02:
When glass rods are rubbed with silk
becomes charged and repels each other.
Example 03:
Plastic rods and fur attract each other, and
the glass rod and silk attract each other.
Example 04:
A plastic pen is rubbed with human air and
then brought near pieces of paper:
(a) What happens when the plastic pen is
brought near the piece of paper?
Answer
The pen picks up pieces of paper. The
papers then drop after sometimes.
This shows that, when a plastic pen is
rubbed with human air acquires a
charge that is able to attract other
substances like piece of papers.
(b) What happens to the pieces of paper on
pen after a few seconds?
Answer
After few seconds pieces of paper falls
off because they acquire similar charges
as the pen.
ORIGIN OF CHARGE
Charges are found in the atom of a material.
All materials are made up of atom which has
electron as negative charge and proton as
positive charge.
When a body is rubbed, it may lose or gain
electrons and cause a body to be charged
positively or negatively.
Types of charges
Positive charge is a charge acquired when
an object loses electron from its atomic
structure.
Negative charge is the charge acquired
when an object gain electrons from an atom.
Note that: An atom has equal number of
electrons (negative charges) and protons
(positive charges). When an atom gains
electrons acquires excess negative charge
and becomes negatively charged, but when
it loses electrons, it remains with excess
protons (positive charges) hence becomes
positively charged.
During rubbing, only electrons are
transferred (are gained or lost).
Example 01
When rubbing an ebonite rod with fur, the
electrons from the fur are transferred to the
ebonite rod.
The far remains positively charged while the
ebonite rod becomes positively charged.
Example 02
When a glass rod is rubbed with silk cloth,
the glass loses electrons and becomes
positively charged and the silk cloth gains
electrons and becomes negatively charged.
Example 03
When one rubs a balloon with a woolen
cloth, the electrons are transferred from the
woolen cloth to the balloon.
The balloon becomes negatively charged
while the woolen cloth becomes positively
charged.
Summary
Material Rubbed with Charge on
the
material
Ebonite Fur / woolen
cloth
Negative
Glass Silk Positive
Polythene Woolen cloth/
fur
Negative
Polystyrene Woolen cloth/
fur
Negative
Perspex Woolen cloth Positive
Celluloses Woolen cloth Positive
Balloon Woolen cloth Negative
Cellulose and polythene are more preferred
to give positive and negative charges
respectively when rubbed with fur because
are less affected by damp conditions.
From the table, note that: when in all cases
the materials acquire negative charge except
for Glass rubbed with silk and when
cellulose and Perspex are rubbed with
woolen cloth.
Example 01
A comb is rubbed with hair and brought near
a small slow stream of air water coming out
from a tape as shown below.
(a) What observation can you make on the
slow stream of water from the tape?
Answer
The stream of water bends.
The water particles are attracted to the
comb, causing the steady stream of
water to bend.
(b) What type of charge was in water?
Water has positive charge.
Because when a plastic comb is rubbed
with hair, it gains electrons from hair
and becomes negatively charged.
Example 02
Two rubber balloons are rubbed with hair.
(a) Will the electric force between one of
the balloons and the hair be attractive
or repulsive? Explain
Answer
The electric force between one of the
balloons and the hair will be attractive
because they acquire different charges.
Unlike charges attract.
(b) Will the electric force between the two
balloons be attractive or repulsive?
Explain.
Answer
The electric force between the two
balloons will be repulsive, because
they acquire the same type of charges.
Like charges repel.
Example 03
(a) State what happen when an ebonite rod
is rubbed with fur.
Answers
The ebonite rod acquires negative
charges.
(b) Explain how a balloon rubbed against
your hair could be attracted to a sheet of
small pieces of paper.
Answer
When the balloon is rubbed against the
hair it acquires negative charges. When
brought close to pieces of paper, the
papers tend to be attracted to the
negatively charged balloon.
ELECTRIC CHARGE
