magnets

2.  Types of magnets:
◦ Permanent magnets retain a magnetic field indefinitely
 Ferromagnetic substances are naturally magnetic
 Magnetite/hematite: naturally occurring iron oxide
 Some transition metals: iron, copper, or nickel.
 Some rare earth metals: neodymium, gadolinium, samarium
◦ Temporary magnets lose their magnetic field strength over time, or
can be turned off and on.
 Magnetized paper clips or needles are paramagnetic (can be
magnetized for a short time)
 Electromagnets become magnetic under the influence of an electric
current
 No longer magnetic when electricity flow is stopped
 Can easily be turned off and on
 …any substance that contains a
magnetic field.

3.  The directional spin of electrons create tiny magnetic regions
called domains
◦ In some atoms, these domains cancel out
◦ In magnets, domains are all lined up in same
direction
 Whenever all electrons spin in the same direction, a
magnetic field is produced

4.  A material such as iron that can be magnetized
because it contains magnetic domains.

5.  A substance that reacts to magnetic fields, but
does not remain so after the field is removed.
 Liquid Oxygen can remain suspended between
two magnets.

6.  Magnetic force =the push or pull a magnet exerts
◦ on another magnet
◦ on iron or a similar metal
◦ or on moving charges (electricity)

7. Magnetic field lines – single magnet
Iron filings lining up along the magnetic field Like poles of two magnets repel each other
Magnetic field lines show attraction
between opposite poles of two magnets

8.  Hold a magnetic field indefinitely.
 Iron, Cobalt, and Nickel are the only substances
that are naturally magnetic.
◦ Co and Ni are somewhat rare, so the vast majority of
magnets are made of iron.
Euro pennies have steel

9.  Electromagnets can easily be
made at home with a copper wire, a
nail, and a battery.
 Wrap the wire around the nail and
hook it to the positive and negative
ends of the battery.
 When electrons flow through the
wire, they induce a magnetic field
around the nail which can then
attract iron objects.

10. Strength controlled by:
◦ Neatness of coiling
◦ Number of loops
◦ Wire gauge (thickness)
◦ Battery strength (more
voltage = stronger)
◦ Magnetic permeability of the
core material
◦ Temperature (colder =
stronger)

11.  An electromagnet starts with a power source and a wire.
◦ Batteries/Electricity produce electrons.
◦ Flowing electrons produce an electric field, which induces a magnetic field.
 Electromagnetic devices are used to change electrical energy into
mechanical energy.
◦ Examples of electromagnetic devices: electric motors, galvanometers, loud speakers,
doorbells, automatic car door locks.

12.  A magnetic field in a current
carrying wire can be increased by
wrapping the wire into a coil. This
coil of wire is called a solenoid
 When a iron core (like a metal
rod) is placed in a solenoid, an
electromagnet is formed
 This is the basis of many
electric motors.

13.  The magnetic field is a dipole field.
◦ That means that every magnet MUST
have two poles (a north and a south
pole).
 Electrical charges are called
monopoles, since they CAN exist
without the opposite charge.

14.  This magnetic field forms circles
around a straight wire carrying
the current.
 Point your thumb in the direction
of the current
 If you curl your fingers around
the wire, the way your fingers
curve is in the direction of the
magnetic field.

15.  If electricity creates a magnetic field, the opposite is
also true!
 When a magnetic field rotates within a coil of wire, it
generates an electric current.
A hand-cranked dynamo charges a battery for an emergency radio…
Or you can have a hamster do it

16.  Use water or wind to turn magnets to
generate electricity

17.  An electric current
flowing around a rod will
make a magnet.
 It is called an
electromagnet
 A moving magnetic field
within a looped wire will
make electricity.
 It is called a generator

18.  The Earth acts as a giant
electromagnet.
 The swirling liquid iron-
nickel outer core moves
around a solid iron-nickel
inner core.
 Electrons moving within
the liquid create an electric
current.
 The electric current
creates a magnetic field
that extends around the
planet.

19.  The moving current around the iron core acts like an
electric current flowing around a core, creating a
strong electromagnetic field.

20.  The Earth’s magnetic field protects us from harmful solar
particles by deflecting or absorbing them.
 The aurora borealis is located at the north pole, because
that is where the energized solar particles come shooting
down into the atmosphere.