Download Chapter 19 Magnetism and Electromagnetism

Chapter 19
Magnetism and
Electromagnetism
Magnets (19.1)
► Magnets
contain a mineral called
“magnetite” also called “lodestones”
► Magnetism= the attraction of a
magnet for another object
► Any shaped magnet has two ends that
are each called a magnetic pole
 One pole will always point north
 One pole will always point south
Interactions between magnetic poles
► Magnetic
poles that are alike REPEL
each other and magnetic poles
that are unlike ATTRACT
each other
► If
you break a magnet in half what
happens??
 Two separate magnets or does it break
into the south pole and north pole…
No, since magnetic field lines are
continuous both inside and outside
the magnetic you get two north poles
and two south poles.
Magnetic Fields
► Magnetic
Field= the region of
magnetic force around a magnet (
allows magnets to interact without
touching)
► Magnetic
Field Lines= map out the
magnetic field around a magnet.
 *they spread out from one pole, curve
around a magnet and return to the other
pole (see figure 5 in book)
The magnetic field can be seen by placing
the magnet under a piece of paper with
small iron filings on top. The filings line up
in the shape of the field, as shown above.
Inside a magnet
► Why
do some materials have strong fields
and some don’t?
 The strength depends on the spinning and
orbiting motion of the electrons ( which make
up lots of tiny magnets)
 Magnetic domain= billions of atoms that all
have magnetic fields that are lined up in the
same way ( all face north pole at same time…
etc.)
a magnetized material all or most of the
domains are arranged in the same direction.
They are ALIGNED
► In
►A
material that shows strong magnetic
effects is said to be a “ferromagnetic
material”
 “ferrum” means iron in Latin
Making Magnets
►A
magnet can be made from a
ferromagnetic material. You can do this by
placing an unmagnetized material in a
strong magnetic field or by rubbing it with a
strong magnet.
 Example: paper clips can be attracted to a
magnetic material when placed in their
magnetic field
► Permanent
magnet = A magnet made of a
material that keeps its magnetism.
► How do you destroy a magnet??
 Magnets lose their magnetism when their
domains become randomly arranged or
unaligned. Ways to destroy it…
►1.
Drop it or strike it hard (knocking out of
alignment)
►2. Heat it to a high temperature (particles
vibrate fast)
► What
happens when you break a magnet?
 When you break a magnet you create another
magnet with it’s own north and south pole.
Magnetic Earth (19.2)
► Compass=
a device that has a magnetized
needle that can spin freely.
- Compass needle usually point North.
Earth as a magnet
► The
Earth has an immense magnetic field
surrounding it, just as there is a magnetic
field around a bar magnet!
► This is why a compass works- the
magnetized needle aligns itself with the
Earth’s magnetic field
Magnetic declination
► The
geographic south and north pole is
different from the magnetic south and north
pole- the angle between the two points (
geographic and magnetic poles) is called the
magnetic declination
 * This changes over time because the magnetic
poles move slowly!!
Magnetosphere
► Earth’s
magnetic field affects the
movements of electrically charge particles in
space… and on Earth!
► Van Allen belts= Two doughnut shaped
regions above the Earth’s surface. These
regions contain electrons and protons
traveling very fast. Not dangerous to us!
► Solar
wind= a stream of electrically charged
particles flowing at high speeds from the
sun. The solar wind helps to shape the
Earth’s magnetosphere
 The magnetosphere is constantly changing due
to solar wind!
Effect of Earth’s magnetic fields
► Because
the Earth produces strong
magnetic fields… it can also make magnets!
► -Causes domains to line up in the same
direction
► Earth’s magnetic field also acts on rocks that
contain magnetic material– creating a
permanent record when the molten rock
hardens.
Electric Current and magnetic fields
(19.3)
► Electric
charge- electrons are negatively
charged(-) and protons are positively
charged (+)
► Electric current= the flow of charge through
a material. The amount of charge is
measured in the ampere or amp or A
 The number of amps tells the amount of charge
flowing past a given point each second
► **An
field!!
electric current produces a magnetic
► Moving
charge and magnetism
 All magnetism is caused by the movement of
charges.
Electric circuits
► Electric
Circuit= a complete path through
which electric charges can flow.
Current ONLY flows through an electric circuit!
A circuit needs three things..
1. a source of electrical energy
2. devices that are run by electrical energy
( ex. Radio, computer, light bulb)
 3. connected by conducting wires and a switch




Conductors and Insulators
► Conductor=
electric currents flow freely
through these materials and are loosely
bound to their atoms
( ex. Copper, silver, iron, and aluminum)
Insulator= a different kind of
material in which charges are not
able to move freely and the atoms
are bound tightly together!
Electrical Resistance
► Resistor=
uses electrical energy as it
interferes with or resists the flow of charge
► Resistance=
the opposition to the
movement of charges flowing through a
material
 Resistance of the material depends on its
atomic structure ( close together vs. spread
out)
► Thomas
Edison used resistance
(current) when he developed
the electric light bulb- he used
Tungsten because it can get
hot enough to glow without
melting!
► Superconductor=
a material that has no
electrical resistance- this means that there
is NO loss of energy!
 Very low temperatures are required for a
superconductor
Why would using superconductors reduce wasted
energy??
Electromagnets
► Solenoids=
A current carrying coil of wire
with many loops, A solenoid creates a
magnetic field that can be turned off and on
by switching the current off and on!
 The north and south poles change with the
direction of the current
Multiplying Magnetism
►A
solenoid with an ferromagnetic core is
called an Electromagnet
 The temporary field of an electromagnet is
produced by the current in the wire and the
magnetized core
 An electromagnet is a strong magnet that can
be turned off and on
► How
do you increase the strength of an
electromagnet?
 1. Increase the current in the solenoid
 2. Add more loops of wire to the solenoid
 3. Wind the coils around the solenoid closer
together
 4. Using a stronger ferromagnetic core
Recording Information
► Electromagnets
are used to record
information onto audiotapes, videotapes,
computer disks and credit cards
 Magnetized particles are put into a pattern that
can later be translated into
information/sound/video.