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Electricity
What is Electricity?
• Electricity refers to the flowing motion
of electric charge.
• Electricity refers to the amount of
imbalance between quantities of
electrons and protons.
• Everything is made of atoms which
contain POSITIVE particles called
PROTONS and NEGATIVE particles
called ELECTRONS.
Electron
m=9.11 x 10-31 KG
Proton
m=1.673 x 10-27
KG
Neutron
m=1.675x10-27KG
•An atom will usually have the same number of
positives and negatives
•This makes the atom NEUTRAL.
Q=Ne
Where:
Q is the electric charge
N is the number of electrons(added or
removed)
e= 1.6 x 10-19 C
Coulumb
e.g #1: What is the value of charge on a
body which carries 20 excess electrons?
N=20
e= -1.6x 10-19 C
As q=Ne
q= 20 * -1.6 x 10-19 C
q= - 3.2 x 10-18 C
Law of Conservation of
It
is possible
to
Electric
Charge
transfer electric charge
During
any
process,
from
one
object
to the
net electric charge of an
another.
isolated system remains
constant(is
conserved)
The
body that
loses
electrons has an excess
Charges
arecharge,
equally while
of
positive
sharedwhen
objects
of
the body, that gains
different charges come
electrons has an excess
into contact w/ each
of
negative
charge
other
• Like charges repel and unlike charges attract
each other.
• Not only can electric charge exist on an object, but it
can also move through an object.
• Conductors are materials that permit electrons to flow
freely from atom to atom and molecule to molecule.
• Insulators are materials that impede
the free flow of electrons from atom to
atom and molecule to molecule.
e.g. #2:When an oil tanker car has arrived at its
destination, it prepares to empty its fuel into a
reservoir or tank. Part of the preparation involves
connecting the body of the tanker car with a metal wire
to the ground. Suggest a reason for why is this done.
History of Electricity
• Early cave people probably recognized the
force of electricity when lightning struck. They
might also have noticed the way amber
attracts light objects, or the way certain fishes,
such as the electric eel, stun their prey.
History of Electricity
• Around 500 B.C. a Greek philosopher named
Thales first discovered electricity when he
learned that when amber is rubbed with
cloth, small bits of straw are attracted.
History of Electricity
• Around 1600, William Gilbert, a physician who lived in
London at the time of Queen Elizabeth I and
Shakespeare, studied magnetic phenomena and
demonstrated that the Earth itself was a huge magnet,
by means of his "terrella" experiment. He also studied
the attraction produced when materials were rubbed,
and named it the
"electric" attraction.
From that came the word
"electricity" and all others
derived from it.
History of Electricity
• In 1752, Benjamin Franklin started
experiments with electricity.
While trying to prove
lightning was electricity he
flew a kite in a lightning storm
with a key at the end and the lightning
touched the key which made a spark.
From this, he made a metal rod to go on a roof
so the houses would have no damage.
History of Electricity
• In 1786, Luigi Galvani discovered
that a dead frog's muscles
twitched when it was placed
near an electrical machine.
He conducted experiments to
try to explain why a dead frog
appeared to jump. Galvani thought the frog's
nerves contained the electricity
History of Electricity
• By 1792, Alessandro Volta, disagreed: he realized
that the main factors in Galvani's discovery were
the two different metals - the steel knife and the
tin plate - upon which the frog was lying. Volta
showed that when moisture comes between two
different metals, electricity is created. This led
him to invent the first electric battery, the voltaic
pile, which he made from thin sheets of copper
and zinc separated by moist pasteboard.
The volt is named after Volta.
History of Electricity
• Voltage(electromotive force(emf) or potential
difference(pd)) – is the electric pressure that
causes current to flow
voltage = energy
charge
or
V = W(joule)
q(coulomb)
History of Electricity
• Charles-Augustin de Coulomb, conducted the
first quantitative work with electric charges.
He studied the magnitude and the direction of
the force between two charged spheres in a
relation to the magnitude of the charges and
distance between them.
• Coulomb’s Law: the force of attraction or
repulsion between two small charged bodies is
directly proportional to the product of the
two charges and inversely proportional to the
square of the distance between them.
F= k(Q1Q2/d2)
where Q1 represents the quantity of charge on
object 1 (in Coulombs), Q2 represents the
quantity of charge on object 2 (in Coulombs),
and d represents the distance of separation
between the two objects (in meters). The
symbol k is a proportionality constant known as
the Coulomb's law constant.
e.G #3: What is the magnitude and direction of
the force on a charge of +4x10-9 C that is 5 cm
from a charge of +5x10-8 C ?
Q1 = +4x10-9 C
Q2= +5x10-8 C
R = 5cm = 5x10-2 C
Find F:
F= k(Q1Q2/d2)
= (9 x 109 N  C2)(4x10-9 C )(5x10-8)
= 1.8 x 10 -6 N m2 / 2.5 x 10-3m2
F= 7.2 x 10 -4 N
History of Electricity
• Michael Faraday invented the electric
motor in 1821.
• Georg Ohm, a German, discovered the
relationship among voltage, current and
resistance in a circuit using direct current.
Ohm’s Law deals with the relationship
between voltage and current in an ideal
conductor.
V= I R
History of Electricity
• In 1878 Joseph Swan, a British scientist,
invented the incandescent filament lamp and
within twelve months Edison made a similar
discovery in America.
History of Electricity
• The recognition of electromagnetism, the
unity of electric and magnetic phenomena, is
due to Hans Christian Ørsted and André-Marie
Ampère in 1819-1820.
• Georg Ohm, a German, discovered the
relationship among voltage, current and
resistance in a circuit using direct current. The
relationship is called Ohm's Law.
Types of Electricity
• made by rubbing together two or more
objects and making friction
• when electrical charges build up on the
surface of a material.
• when something gives up or gains electrons
• objects may be attracted to each other or may
even cause a spark to jump from one to the
other.
Types of Electricity
Friction - the force between two surfaces rubbing
together.
Conduction
transfer of electrons from a charged object to
another object by direct contact.
Induction
the movement of electrons to one part of an
object by the electric field of another.
Types of Electricity
• the flow of electric charge across an electrical
field.
• Free electrons continuously move to spaces
where electrons are missing.
• generated by batteries and power plants.
Types of Electricity
references
• http://library.thinkquest.org/J001647F/
• http://library.thinkquest.org/6064/history.htm
l
• http://www.electricityforum.com/electricityhistory.html