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Electromagnetism
Behavior of Charges
Magnetism
•Magnetism is a class of physical
phenomena that includes forces exerted by
magnets on other magnets.
•The earliest magnets were found naturally in the
mineral magnetite which is abundant the rock-type
lodestone. These magnets were used by the ancient
peoples as compasses to guide sailing vessels.
•Magnets produce magnetic forces and have magnetic
field lines
What is a magnet?
It is a substance that contains a magnetic field.
There are three primary types of magnets:
Ferromagnetic- A substance that is naturally and
permanently magnetic like iron.
Paramagnetic- which becomes magnetic under
the influence of a magnetic field.
Electromagnet- Becomes magnetic under the
influence of an electric current. Is no longer
magnetic when electricity flow is stopped.
Magnets
Ferromagnets
Paramagnet
Electromagnet
Magnets have two ends or poles, called north
and south poles. At the poles of a magnet, the
magnetic field lines are closer together.
Magnetic field =surrounds a magnet and can exert
magnetic forces.
Unlike poles of magnets attract each
other and like poles of magnets
repel.
Permanent Magnet
• A permanent magnet is a substance that
holds a magnetic field indefinitely.
• Iron, Cobalt, and Nickel are the only
substances that are naturally magnetic.
• But, Co and Ni are somewhat rare, so the vast
majority of magnets are made of iron.
Euro pennies have steel
The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a magnetic
field much like a bar magnet.
What are magnetic domains?
Magnetic substances like iron, cobalt, and nickel are
composed of small areas where the groups of atoms are
aligned like the poles of a magnet. These regions are called
domains.
All of the domains of a magnetic substance tend to align
themselves in the same direction when placed in a
magnetic field. These domains are typically composed of
billions of atoms.
Electricity and Magnetism – how are they
related?
When an electric current passes through a wire a
magnetic field is formed.
What is an electromagnet?
When an electric current is passed through a coil
of wire wrapped around a metal core, a very
strong magnetic field is produced. This is called
an electromagnet.
Electromagnetic devices:
• 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.
Electromagnets
• 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.
• Suddenly the nail is magnetic
and can attract iron objects.
SOLENOID
• 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 magnetic core is
placed in a solenoid, an
electromagnet is formed
• This is the basis of
many electric
motors.
What is a galvanometer?
A galvanometer is an electromagnet that interacts with a
permanent magnet. The stronger the electric current
passing through the electromagnet, the more is interacts
with the permanent magnet.
Galvanometers are
used as gauges in
cars and many other
applications.
The greater the current passing through the wires, the stronger the
galvanometer interacts with the permanent magnet.
What are electric motors?
An electric motor is a device which changes electrical energy
into mechanical energy.
How does an electric motor work?
Go to the next slide 
We have seen how electricity can produce a magnetic
field, but a magnetic field can also produce electricity!
How?
What is electromagnetic induction?
Moving a loop of wire through a magnetic field
produces an electric current. This is electromagnetic
induction.
A generator is used to convert
mechanical energy into electrical energy by
electromagnetic induction.
Direct current versus alternating current –
AC vs DC : What’s the difference?
Direct current is electrical current which comes
from a battery which supplies a constant flow of
electricity in one direction.
Alternating current is electrical current which
comes from a generator. As the electromagnet
is rotated in the permanent magnet the
direction of the current alternates once for
every revolution.
Right Hand Rule
• This magnetic field forms circles
around a straight wire carrying
the current.
• Point your thumb in the
direction of the current (which is
toward the negative terminal)
• If you curl your fingers around
the wire, the way your fingers
curve is in the direction of the
magnetic field.
Electric Generator (Dynamo)
• The opposite of an electromagnet is also true also!
• When a magnetic field rotates around a 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
Turbines
• Use water or wind to turn magnets to
generate electricity
To summarize
• An electric current flowing
around a rod will make a
magnet.
• A moving magnetic field
flowing around a wire will
make electricity.
• It is called a generator
• It is called an electromagnet
Quick Quiz
• Electricity and magnetism are both aspects of
A. the north pole.
• B. the south pole.
• C. electromagnetic force.
• D. ferromagnetic material.
Quick Quiz
• Electricity and magnetism are both aspects of A.
the north pole.
• B. the south pole.
• C. electromagnetic force.
• D. ferromagnetic material.
• When electric charges are moving through a wire,
a magnetic field is created. The wires are made
out of materials/metals that can be magnetized.
Quick Quiz
• A fan uses a rotating electromagnet to turn its
blades. This is an example of
• A. magnetic poles.
• B. an electric motor.
• C. a galvanometer.
• D. a loudspeaker.
Quick Quiz
• A fan uses a rotating electromagnet to turn its
blades. This is an example of
• A. magnetic poles.
• B. an electric motor.
• C. a galvanometer.
• D. a loudspeaker.
Ferromagnetic material
• A material such as iron that can be magnetized
because it contains magnetic domains.
Paramagnetic material
• 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.
Earth as a magnet
• The Earth acts as a giant
electromagnet.
• There is a swirling liquid
iron-nickel outer core
floating around a solid
iron-nickel inner core.
• Electrons moving around in
the liquid create an electric
current.
Earth as a magnet
• The moving current around the iron core makes
for a giant magnetic field.
• This acts much like a magnet flowing around a
wire, creating a strong magnetic field
Earth’s Magnetic Field
• 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.
Aurora Borealis