Have you ever stuck a balloon to the
wall after rubbing it on your head?
Has your sweater ever made crackling noises when you took it off?
Have you ever got an electric shock off your door knob?
All these things happen
because of
Static
What is Static Electricity?
Static electricity occurs when there is a build up of electric charge on the
surface of a material.
It is called static electricity because the charges don’t move.
Charge can be either positive or
What is charge?
To understand charge we have to look at things on an extremely small scale.
We have to try and understand things that we can’t even see with the most powerful microscope.
The atom
Everything we see around us everyday is made of atoms.
We can’t see individual atoms because
they are so small.
In fact the diameter of an atom is about 0.0000000001m
What is inside the atom?
The atom is made of 3 sorts of particles.
The electron The proton The neutron
Inside an atom
The protons and neutrons sit
together in a lump in the middle called the nucleus.
The electrons orbit around the
nucleus, a bit like the planets orbiting the Sun.
Most of the atom is empty space if atoms were the size of football fields, the nucleus would be a grain of sand in the middle and the electrons would be orbiting around the edge.
Atoms Are
Everywhere
Electrons move in and out of fixed pathways around the
nucleus
Changing the number of electrons in a particular type of
On the Move
Electrons in the outer rings or shells of atoms
are bound more loosely to the nucleus
Such electrons tend to break free from the
nucleus and wander around amongst other nearby atoms
Charge
The electron is negatively charged.
The proton is positively charged.
Charge
Most things have the same number of electrons and protons in them.
They don’t have any overall charge.
If this isn’t true interesting things can
How do charges behave?
What do you know about magnets?
2 north poles will repel each other, but a north and a south put together will attract one another.
How do charges behave?
Exactly the same thing happens with charges.
2 positive charges put together will repel each other.
Put a positive charge near a negative charge and they will attract each
other.
A charged object may even attract a
Static electricity
Static electricity is caused when
certain materials are rubbed against each other.
Electrons can be rubbed off one material and on to another.
The material that has got extra
electrons is now negatively charged
Electric Charge
Two kinds:
positive and negative (terms coined by Benjamin Franklin)
When you rub a glass rod with silk, the charge
that is left on the glass was called positive. If you rub a hard rubber rod with silk, the charge left on the rod was called negative.
Static electricity
It is this imbalance of positive and negative charges that causes:
Balloons to stick to walls.
Your hair to stand on end when brush
your hair on a dry day.
Law of Electrostatics
Like charges repel
Opposite charges attract
Neutral objects
Text work
Read p 465 -471
Electrostatic Series
The electrostatic series is a list that can be used to predict the transfer of electrons from friction.
A substance higher on the list will always lose electrons and become
Electrostatic Series
(Weak hold on electrons)
Acetate Glass Wool Fur Calcium, magnesium, lead Silk Aluminum, zinc Cotton Paraffin wax Ebonite Polyethylene (plastic) Carbon, copper, nickel Rubber
Sulphur
Platinum, gold
(Strong hold on electrons)
Question:
By mistake a silk blouse and a pair of wool socks are put into a clothes dryer. What charge will appear on the blouse when it rubs against the socks?
Items further apart on the list will transfer more electrons than items closer on the list and build up a
Creating charge
Objects may be charged by:
•conduction (requires contact with another charged object.
•induction (requires no contact with another
charged object).
Friction
When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings.
Like the shoes rubbing against the carpet.
When a charged object comes in
contact
with a neutral object, some of
the
electrons are transferred
between
the objects.
When a
negatively charged rod touches this
neutral sphere, some of the
When a positively charged rod touches this neutral sphere, some of the
electrons from the sphere move into the positively charged rod. The sphere
becomes positive.
+ - - +
11.4
Classes of Materials
CONDUCTORS are materials in which charges may move freely (e.g. copper).
INSULATORS are materials in which
charges cannot move freely (e.g. glass).
11.6
Induced Charge
Charged objects brought close to but not touching a conductor may cause charge to redistribute (polarize the conductor).
If a polarized conductor is momentarily
The van de Graaf generator (large silver ball) deposits electrons on the ball. When a person places their hand on the ball and the machine is turned on, electrons are transferred to and
collected on the person touching the silver ball.
Why do you
think this
machine
affects the
hair of the
Electroscopes
Metal-leaf Electroscope
A small metal ball connected to a
metal rod. Hanging from the rod are two thin metal strips called leaves.
Because the parts of the
electroscope are made of metal electrons can move freely within it.
Physlink Science Store.
http://www.physlink.com/estore/cart/GoldF oilElectroscope.cfm. 2007
Pith-ball Electroscope
A small ball hanging by a thin thread.
Because the ball is
very light it moves in response to small
electric forces. School Store.
