1. Magnetism and Electromagnetism
• The Nature of Magnets
• Earth As a Magnet
• Magnetism in Action
• Magnetism From Electricity
• Electricity From Magnetism

2. The Nature of Magnets
• The Greeks first discovered magnetism.
• Magnetism is the force of attraction or
repulsion caused by magnetic
materials.
• Every magnet has two poles: North and
South.
• Opposite poles attract and like poles
repel.

3. The Nature of Magnets
• The area over which magnetic force is
applied is called the magnetic field.
• Magnets can be temporary or
permanent.
• Many permanent magnets are created
from mixtures of aluminum, nickel,
cobalt, and iron (Alnico).

4. The Nature of Magnets
• The atomic structure of groups of atoms
determines their magnetic properties.
• When atoms line up similarly they
create a magnetic domain.
• When groups of domains line up, the
object becomes magnetic.

5. The Nature of Magnets
• Striking or heating magnets can mix up
their domains, causing them to lose
their magnetic properties.
• Similarly, exposing substances to
magnets can causes their domains to
line up and give them magnetic
properties.

6. The Earth As a Magnet
• The earth exerts magnetic forces which
are strongest near its poles.
• The magnetism is believed to be
caused by the motion of iron and nickel
in the earth’s core.
• Scientists have also been able to tell by
examining rocks that the earth’s
magnetic field has reversed many times
in it’s history (every 500,000 years).

7. The Earth As a Magnet
• Compasses are small magnets which
align themselves with the earth’s
magnetic field and are used to help find
direction.
• The north pole of a magnet points in the
northward direction, meaning that the
geographic North Pole is actually a
magnetic south pole.

8. The Earth As a Magnet
• In addition, the magnetic and
geographic poles do not line up.
• They are actually 1500 kilometers from
each other.
• The angular difference of the poles is
called magnetic variation or declination.
• This must be taken into account when
using a compass.

9. The Earth As a Magnet
• Generally, the closer a compass is
to the equator, the more accurate it
is.
• Other planets and even our sun
have magnetic fields.
• Our sun’s magnetic field is thought
to play a role in the sunspot cycle.

10. Magnetism in Action
• The earth’s magnetic field deflects
charged particles radiated from the sun.
• The region of the earth’s atmosphere
where the magnetic field lines run is
called the magnetosphere.
• The interactions can cause the northern
and southern lights (aurora borealis and
australis).

11. Magnetism in Action
• These same types of interactions
allow astronomers to use radio
waves when studying stars.
• Additionally, magnetism is used to
confine hot plasmas used in
nuclear fusion (an energy source
scientists are trying to perfect).

12. Magnetism From Electricity
• In the 1800’s Hans Oersted discovered
that a current carrying wire would
deflect the needle of a compass.
• He inferred that an electric current
would induce a magnetic field with
direction dependent upon that of the
current.

13. Magnetism From Electricity
• In playing with his new discovery,
Oersted found that twisting the wire into
loops (a solenoid) would create a strong
magnetic force.
• By placing an iron core inside the
solenoid, an even stronger magnetic
force can be generated.
• This combination is called an
electromagnet.

14. Magnetism From Electricity
• Electromagnets are strong
temporary magnets that can be
turned on or off.
• Since forces always occur in pairs,
the wire not only exerts a force on
the magnet, but magnets exert a
force on the current carrying wire.

15. Magnetism From Electricity
• There are many practical applications of
Oersted’s discovery.
• Electric motors use electromagnets that
are free to rotate called armatures.
• The armature sits in between the pole
of a permanent magnet and spins by
being attracted and repelled by
constantly changing its poles due to an
AC circuit.

16. Magnetism From Electricity
• DC circuits can also be used in
electric motors when a device
called a commutator is incorporated
in the electromagnet to continually
switch the direction of the current.

17. Magnetism From Electricity
• A galvanometer is another device
that relies on electromagenetism.
• Galvanometers measure current
strength and direction.
• Other uses of electromagnetism
include doorbells, car starters,
telephones, and telegraphs.

18. Electricity From Magnetism
• After scientists learned of Oersted’s
discovery, many wondered if
electricity could be produced from
magnetism.
• In 1831 two scientists, working
independently, found it to be
possible: Michael Faraday and
Joseph Henry.

19. Electricity From Magnetism
• Faraday found that a changing
magnetic field would induce an
electric current in a wire through
a process called
electromagnetic induction.

20. Electricity From Magnetism
• Electric generators, the type used
at power plants to create our
electricity, use electromagnetic
induction to produce electricity.
• When a power source spins a
turbine, electromagnets are spun
between coils of wire creating an
electric current in the wire.

21. Electricity From Magnetism
• The resulting current produced
is alternating current.
• It is carefully setup so that the
current changes direction 120
times/sec or at 60Hz
(cycles/sec).

22. Electricity From Magnetism
• Transformers are devices that
increase or decrease voltage in
a wire.
• Two insulated wires are wound
around the same iron core the
alternating current in one
induces a current in the other.

23. Electricity From Magnetism
• If the induced wire has fewer
coils (step down transformer),
the voltage is decreased.
• If the induced wire has greater
coils (step up transformer), the
voltage is increased.

24. Electricity From Magnetism
• Power companies use these
transformers to transmit high
voltage electricity to your street
and then step it down before
being transferred to your house.