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Electricity
Harnessing energy for a
better life
Electric Charges
 Matter is made of atoms,  Electrons can be moved
from one atom to
which are made of
another, but protons
electrons, protons, and
cannot move.
neutrons.
 Electrons have a negative  When an atom has gained
electrons, it is negatively
charge, and protons have
charged.
a positive charge.
 When an atom has lost
electrons, it is positively
charged.
 Rule of Charge:
Opposite charges attract,
and like charges repel.
Charge and Force
 Electrons can be rubbed  Like charges repel each
off of one object and onto other, and unlike charges
another. The objects get attract each other. The
area around a charge
a static charge.
where you can feel force is
 When neutral objects are
called the electric field.
rubbed together and
 The electric field is
charges are rearranged,
strongest when you are
the objects get unlike
closest to the charge and
charges, and they stick
gets weaker as you get
together.
farther away from the
charge.
Static Electricity
 A neutral object builds up  Charging by friction
a static charge by gaining
happens when objects
or losing electrons.
rub together and
 An electroscope can be
electrons are transferred.
used to tell detect a static  Charging by conduction
charge.
happens when a charged
 Static electricity can be
object touches another
caused in 3ways: friction,
object and electrons are
conduction, or induction.
transferred.
 Charging by induction
happens when a charged
object held close to
another object causes
charges to be
rearranged.
Conductors and Insulators
 Most metals are good
 Materials through which
conductors because of their electrons cannot move
electrons can move from
easily are called
atom to atom in a “sea of insulators.
electrons.”
 Electrons are tightly
 Acids, salt water and tap
bound to the atoms of
water are also good
good insulators and
conductors of electricity.
cannot move from atom
Pure distilled water does
to atom.
not conduct electricity.
 Wood, ceramic, rubber,
 Materials through which
glass, and many plastics
electrons can move easily
are good insulators.
are good conductors.
Charges can build up on
the surface of good
insulators, and stay there
as a static charge.
Lightning!
 When a highly charged
cloud is over land,
 During a storm, water and
another charged area on
dust particles are rubbed
the ground is produced
together by winds. Static
charges build up because of by induction. Charges
are now separated!
friction.
 Charged areas of the clouds Lightning is caused by
the discharge
touch other areas, and
(equalization) of this
charged particles are
transferred within clouds by static electricity.
conduction.
Electric Current
 Electric current happens when  Electrochemical cells
electrons move, or flow
and thermocouples
through a wire or some other
cause the voltage
kind of conductor.
that makes electrons
flow. These devices
 For electricity to flow, you
need a closed continuous path, are sources of free
electrons.
called a circuit.
 You also need a difference in  There are two kinds
of electrochemical
charge from one end of the
cells---wet cells (a
wire to the other that pushes
car battery) and dry
the electrons through the
cells (flashlight
conductor. This is called
batteries).
voltage.
Types of Current
 AC and DC current: When the electrons flow in only
one direction through a conductor, this is called direct
current, or DC. When electrons first go in one
direction, then back, then forward again, this is called
alternating current, or AC.
 Current from batteries is DC, and current from electric
power plants is AC.
DC
electricity
comes
from
here!
AC
electricity
comes
from here!
Types of Circuits
A circuit in which the  A circuit in which the
current must pass
current can travel
through all of the
through more than
resistors on only one
one path is called a
path is called a series parallel circuit.
circuit.
Ohm’s Law
Three things can be measured when electrons flow
through a circuit.
1)
2)
3)
How many electrons flow

through the circuit each second
is called current. The letter I
stands for current. Current is

measured in amperes (A).
The “push” behind electrons in a
circuit is called voltage. The
letter V stands for voltage.
Voltage is measured in volts
(V).
The force opposing the flow of
electrons through a circuit is
called resistance. The letter R
stands for resistance.
Resistance is measured in ohms
(Ω).
Lights, radios, and other
electric appliances cause
resistance in a circuit.
Ohm’s Law shows the
relationship between
these things and says:
I= V/R
V
I R
Electric Power and Safety
 Electric power and electric
Be safe when using
energy can be calculated
electricity!
using the following formulas:  Never remove the
P
P = V I
ground wire from a
V I
plug.
Power = voltage times current  Never use electric
appliances near water,
E
E = P t
because water is a
P t
conductor!
Energy = power times time
 Never overload
circuits or replace
burned out fuses with
pennies. This can
cause a short circuit,
which could start a
fire.