Transcript Electricity and Magnetism

Electricity and
Magnetism
Atom Review
 Electrons
charge (-)
 Protons
have a negative
have a positive
charge (+)
Like charges repel each
other
Unlike charges attract
each other
electric field: the field around
charged particles that exert
force on other charged
particles
A charged particle in the
electric field of
another particle will
either be pushed or
pulled, depending on the
charge.
Static Charge
 Protons
are bound tightly
in the nucleus of an atom,
but electrons can
sometimes leave the atom
Insulator: a material
through which charges of
an electrical current are
not able to move
Ex. wood, rubber, glass
Conductor: A material
through which electrons can
move freely
Ex. copper, gold, aluminum
 If
an object loses
electrons, then it has an
overall positive charge.
 If
an object gains
electrons, then it has an
overall negative charge.
static electricity: the
buildup of charges on an
object
 Van
de Graaf generator:
produces static electricity
Charges can be transferred
to one another in three
ways:
1. friction
2. conduction
3. induction
Friction: transfer of electrons
by rubbing
Conduction: transfer of
electrons from one
object to another by
direct contact
Induction: movement of
electrons to one part of
an object caused by the
electric field of another
object
Law of Conservation of
Charge: Charges cannot be
created or destroyed.
Electrons can only be
transferred from one object
to another.
Examples of static
electricity:
 Static cling in the dryer
 Plastic wrap
When a negatively
charged object and a
positively charged object
come together, the
electrons move until the
charges balance out
static discharge: the loss of
static electricity as electrons
move off an object
- this can also be called
GROUNDING
Examples of static discharge:
 shock from walking across a carpet
and touching something made of
metal
 lightning
Electrical Safety
-
-
It is always better to err on
the side of caution – if you see
lightning and you are outside –
GET INSIDE
Always turn off electricity at
the circuit breaker before
attempting home repairs
-
-
the 3rd prong found in most
electrical outlets is for the
“ground” wire; it provides a path
for electricity to reach the ground
in case of a surge (it helps to
protect both the equipment and
helps to prevent electrical fires
within the walls of your home)
Under NO circumstances should
you EVER remove the 3rd prong of a
cord to fit a plug into a 2 prong
outlet
Electrical
Circuits
electrical potential: the
potential energy per unit
of electrical charge
voltage: the difference in
the amount of electrical
potential between 2 objects
- measured in volts (V)
voltmeter: device used to
measure voltage
Electrons will flow as long
there is a difference in the
electrical potential
 Voltage
causes current to
flow through an electrical
circuit
electrical circuit: a
complete path through
which electrical charges can
flow
voltage source: creates a
potential energy difference
in an electrical circuit
ex. batteries and generators
current (I): the flow of
electric charges through a
material
measured in Amperes (A)
ammeter: device used to
measure current
resistance: the opposition to
the movement of electric
charges through a material
measured in Ohms ()
- depends on the thickness
and length of a wire, as
well as how well the
material conducts
electricity
resistor: a device in
electrical circuits that
uses electrical energy as
it interferes with the
flow of electric charge
The greater the
resistance, the less
current there is for a
given voltage
 If
an electrical current
can travel through one of
two paths, it will choose
the “path of least
resistance”
Inside an XBox 360
Ohm’s Law
Resistance = Voltage
Current
OR
V
I
R
Types of Circuits:
Series & Parallel
Series Circuit: a circuit
where there is only one path
for the current to take
- all parts of the circuit are
connected one after another
A series circuit
ex. Xmas tree lights - if one
bulb burns out, the whole
strand goes out because
there is no other path for
the current to take
When more resistors, (ex.
light bulbs) are added to the
circuit, the light becomes
dimmer.
Remember! If resistance
increases, then current
decreases. Therefore, the
bulbs will burn less brightly.
Parallel Circuit: a circuit
that has several paths for
the current to take
- different parts of the
circuit are on separate
branches
A parallel circuit

If one bulb burns out, the
rest of the lights stay on
because the current can
move through the other
branches.
As additional resistors are
added, the brightness of
the light does not change
Electromagnetism
magnetism: the attraction of
a magnet for another object
magnetic pole: the area of a
magnet where the magnetic
effect is the strongest
Poles that are alike
repel each other, poles
that are unlike attract
each other.
magnetic field: region
of magnetic force
around a magnet
magnetic domain: a
cluster of billions of
atoms that all have
magnetic fields that
are lined up in the
same way
•In a magnetized
material, all or most of
the domains are arranged
in the same direction
 That
means that all the
domains are aligned!
Magnets can lose their
magnetic properties by
being dropped, struck
hard or heated.
(the domains are knocked
out of alignment)
When a magnet is
broken in half, it does
NOT lose its
magnetism, it simply
becomes 2 magnets!
An electric current
produces a magnetic
field.
solenoid: a current carrying
coil of wire with many loops
- creates a magnetic field
that can be turned on and
off
electromagnet: a strong
magnet that can be turned
on and off
Examples of electromagnets:
- solenoid
- junkyard crane
- tape recorder
Generating Electricity
An electric current will be
produced in a conductor
when the conductor moves
across the lines of a
magnetic field.
electromagnetic induction:
the process of generating an
electric current from the
motion of a conductor
through a magnetic field
The flow of an induced
current may be
constant or may
change direction
alternating current (AC): a
current consisting of charges
that move back and forth in a
circuit
ex. the circuits in your home
direct current (DC):
current consisting of
charges that flow in one
direction
ex. battery