Download Electromagnets & magnetism

Advanced Physical Science
Magnetism
Magnetism: The ability of some substances to
attract iron, steel, and some other metals
 Magnetism is a property of moving e Every moving e- has a magnetic field around it
 Each e- in every atom is a tiny magnet

Magnetic Domain
 Electrons are negatively charge
particles that move around the
nucleus of atoms
 Moving electrons produce magnetic
fields that give atoms a N and S pole
 In most materials (like Copper and
Aluminum) magnetic fields cancel
each other out. Result: the object is
not magnetic
Magnetic Domain (cont)
In some materials (like iron, nickel and
cobalt), the atoms group together in tiny
regions called domains.
 Domains are like tiny magnets of
different sizes within an object.

Magnetic Poles

Like poles repel

Unlike poles attract

Broken magnets create new poles
Magnetic Field
Area around a magnet where magnetic
forces act
 Forces are in a specific direction shown by
field lines
 The lines map the strength of the magnetic
field (stronger at poles)

Iron filings placed around a magnet
will show the shape of the magnetic
field around the magnet
Permanent Magnets
Made from magnetic material (an alloy
of aluminum, nickel, and colbalt) and
have a persistent magnetic field
 Retain magnetic properties better than
other materials
 A strong current is used to align the
domains of the alloy
 Once the domains are lined up, they
tend to remain that way

Making a Magnet
A magnet can be made by
aligning domains in an object
 Example: An iron nail can be
magnetized if you rub it in one
direction with one pole on a
magnet
 The magnetic field of the
magnet will cause the domains
in the nail to rotate and align
with the magnet

Losing Magnetism
Magnets can lose magnetism if domains of
a magnets become unaligned
 Things that cause magnet to get out of
alignment:
 Dropping a magnet
 Heating a magnet

Magnetism from Electricity
An electric current will produce a
magnetic field
 Electromagnetism: The interaction
between electricity and magnetism

Magnetism from Electricity:
Solenoids
A coil of wire that produces a magnetic field
when carrying an electric current
 Increase strength of magnetic field produced
by solenoid by…
 Adding more loops
 Increasing the current
in the wire

Magnetism from Electricity:
Electromagnets
Temporary magnet formed by placing iron
inside a current carrying wire (electricity)
 Magnetic field is only present when current
is flowing
 Strength of magnetic field is increased by
adding more turns of the wire or by
increasing the amount of current
through the wire.
 Magnetic properties can be
controlled by changing the current.

Examples of Electromagnets
Press the doorbell, switch in solenoid circuit
closes, electric current created, iron rod is
pulled through solenoid, rod strikes bell
Electromagnet in a salvage
yard, turned on and off to lift
scrap metal
Maglev Train, Japan
Electricity from Magnetism:
Electromagnetic Induction



Magnetic Field can
produce an electric
field
The size of electric
current depends…
 Number of wire
loops
 How fast move
magnet
The direction
depends on
 Whether magnet is
pulled or pushed
Electricity from Magnetism
(cont)
In previous example,
electric current
induced by moving
the magnet
 Electric current can
also be induced by
moving the wire

Application of Electromagnetic
Induction: Generator
Converts MECHANICAL ENERGY to ELECTRICAL
ENERGY
 A generator rotates a coil of wire through a magnetic field
 The changing magnetic field around the wire induces
electric current in the wire
 The electric current produced
by a generator changes
direction each time the
coil makes a ½ turn
ALTERNATING
CURRENT (AC)
http://www.generatorguide.net/howgeneratorworks.html

Transformer
Increases or decreases the voltage of an
alternating current
 Consists of 2 coils wrapped around an iron ring
 Step-up transformer: Increases voltage
 Step-down transformer: Decreases voltage

Electrical Energy to your Home
Generator at the power plant produces
electric current with HIGH voltage
 Step-up transformers increase the
voltage in order to decrease loss of
POWER that occurs during transmission
over long distance
 Step-down transformers decrease the
voltage before the electric current
reaches consumers

How Electricity Gets to Your
House




Electricity is made at a power plant by huge
generators (HIGH voltage) Most power plants
use coal, but some use natural gas, water or
even wind.
The current is sent through transformers to
INCREASE THE VOLTAGE to push the power
long distances.
The electrical charge goes through highvoltage transmission lines that stretch across
the country.
It reaches a substation, where the VOLTAGE
IS LOWERED so it can be sent on smaller
power lines
How Electricity Gets to your
House (cont.)




It travels through distribution lines to your
neighborhood, where smaller pole-top transformers
reduce the voltage again to take the power safe to
use in our homes.
It connects to your house through the service drop
and passes through a meter that measures how
much our family uses.
The electricity goes to the service panel in your
basement or garage, where breakers or fuses protect
the wires inside your house from being overloaded.
The electricity travels through wires inside the walls to
the outlets and switches all over your house.
FYI…Nuclear Power Plant
Thermal Energy from a nuclear reaction
boils water to produce steam
 The steam turns a turbine
 The turbine turns the magnet of the
generator, inducing electric current and
generation electrical energy.
