Electricity
Electric Charges
 Matter is made of atoms, which in
turn are made of electrons,
protons, and neutrons.
 Electrons have a negative charge,
and protons have a positive
charge. Neutrons have no
charge.
 Electrons can move from one
atom to another, but protons
cannot move .
 When an atom has gained
electrons, it has more electrons
than protons, and it is negatively
charged.
 When an atom has lost electrons,
it has more protons than
electrons, and it is positively
charged.
 Rule of Charge: Opposite charges
attract, like charges repel.
Charge and Force
 Electrons can be rubbed off of one 
object and onto another. The
objects then get a static charge.
 When neutral objects are rubbed
together and charges are
rearranged, the objects get unlike 
charges, and they stick together.
Like charges repel each other, and
unlike charges attract each other.
The area around a charge where
you can feel force is called the
electric field.
The electric field is strongest when
you are closest to the charge.
Charged balloon sticks to
charged area of a wall.
Static Electricity
 A neutral object can build up a  Static electricity can be caused in
static charge by gaining or
3ways: friction, conduction, or
losing electrons.
induction.
 An electroscope can be used to  Charging by friction happens when
tell detect a static charge. It
objects rub together and electrons
cannot tell if the charge is
are transferred.
positive or negative.
 Charging by conduction happens
when a charged object touches
another object and electrons are
transferred.
 Charging by induction happens when
a charged object is held close to
another object and that causes
charges to be rearranged.
Conductors and Insulators
 Materials through which

electrons can move easily are
good conductors.
 Most metals are good conductors 
because of their metallic bonds
and their “sea of electrons.”
 Acids, sea water , and tap water 
are also good conductors of
electricity. Distilled water does
not conduct electricity.
Materials through which electrons
cannot move easily are called
insulators.
Electrons are tightly bound to the
atoms of good insulators and cannot
move around.
Wood, ceramic, rubber, glass, and
many plastics are good insulators.
Charges can build up on the surface
of good insulators, and stays there
as a static charge.
Lightning!
 During a storm, water and dust

particles are rubbed together by
winds. Charges build up in the
clouds because of this friction.
 Charged areas touch other areas of 
the clouds, and some charges are
transferred within clouds by
conduction.
When a highly charged cloud is
over land, a charged area on the
ground is produced by induction.
Charges are now separated!
Lightning is caused by the
discharge (equalization) of these
separate static electric charges.
- charge
- charge
+ charge
- charge
+ charge
- charge
Electric Current
 Electric current happens when
 Electrochemical cells and
electrons flow through a wire or another
thermocouples cause the
conductor.
voltage that makes electrons
flow.
 For electricity to flow, you need a closed
continuous path, called a circuit.
 There are two kinds of
electrochemical cells---wet
 You also need a difference in charge
cells such as a car battery
from one end of the wire to the other
and dry cells like flashlight
that pushes the electrons. This is called
batteries.
potential difference or voltage.
Types of Current
 There are two types of electric
current--AC and DC current.
 When the electrons flow in only
one direction, this is called direct
current., or DC.
 Current from batteries is always
direct current.
 When electrons first go in one
direction, then reverse, then
back again, this is called
alternating current, or AC.
 Current from generating plants
that powers our homes and
businesses is alternating
current.
Ohm’s Law
 The “push” behind electrons in a
 Ohm’s Law relates the push behind
circuit is called voltage. The letter V
electric current to the number of
stands for voltage. The unit for
electrons flowing and to the
voltage is Volts (V).
resistance to their flow.
 The force opposing the flow of
 The rate of electrons flowing through
electrons through a circuit is called
a circuit is called current. The letter I
resistance. The letter R stands for
stands for current. Current is
resistance. The unit for resistance
measured in electrons per second or
is the Ohm (Ω)
Amperes or amps (A).
 Ohm’s Law says:
I= V/R
V
I
R
Types of Circuits
 A circuit in which the current must  A circuit in which the current can
pass through all of the resistors on
travel through more than one path
only one path is called a series
is called a parallel circuit.
circuit.
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Electric Power and Safety
 Electric power and electric energy Be safe when using electricity!
can be calculated using the
 Never remove the ground wire
following formulas:
from a plug.
 P = V I Power = (voltage)(current)
 Never overload circuits or
 E=Pt Energy = (power)(time)
replace burned out fuses with
pennies. This can cause a short
P
E
circuit, which could start a fire.
V
I
P
t
 Never use electric appliances
near water, because tap water is
a conductor!
 Stay away from windows and
electrical appliances during
thunder storms.