Transcript What is magnetism? - Model High School

What is magnetism?
Magnetism is the force of attraction
or repulsion of a magnetic material
due to the arrangement of its atoms,
particularly its electrons.
What is Magnetism?
• Magnets have been known for
centuries.
• The Chinese and Greeks knew
about the “magical” properties of
magnets. The ancient Greeks
used a stone substance called
“magnetite.” They discovered that
the stone always pointed in the
same direction. Later, stones of
magnetite called “lodestones”
were used in navigation.
What is Magnetism?
• Magnets produce magnetic forces
and have magnetic field lines
Magnets have two ends or poles, called north and
south poles. At the poles of a magnet, the magnetic field
lines are closer together.
Unlike poles of magnets attract
each other and like poles of
magnets repel.
Magnetic Fields
The area around a magnet
where magnetic forces act
Magnetic Lines of Force
• Imaginary lines that show the shape of the
magnetic force.
– Closest at the poles
where magnet is the strongest.
Like repels
like…
Opposites attract!
Poles of a magnet
always
Come in pairs!
If you cut a magnet in half,
S
N
S
you get 2 magnets!
N S
N
If you cut it again,
you get more magnets . . .
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.
Magnetic Domains
Atoms themselves have magnetic properties due
to the spin of the atom’s electrons.
Groups of atoms join so that their magnetic fields
are all going in the same direction
These areas of atoms are called “domains”
Magnetic Domains
When an unmagnetized substance is placed in a magnetic
field, the substance can become magnetized.
This happens when the spinning electrons line up in the
same direction.
How to break a magnet:
1. Drop it
2. Heat it
This causes the domains to
become random again!
Temporary Magnets
William Gilbert, an
English physician, first
proposed in 1600 that the
earth itself is a magnet,
and he predicted that the
Earth would be found to
have magnetic poles.
The Earth is a magnet:
It exerts magnetic
forces and is
surrounded by a
magnetic field
that is strongest
near the
North and South
magnetic poles
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.
We use the Earth’s magnetic field
to find direction.
The needle of a compass always points
toward the magnetic south pole.
We call this direction “North”
(remember, opposites attract)
The sun has a magnetic field, too.
It extends far above the sun’s
surface.
Other planets in the solar
system also have these
magnetic fields
When a charged particle enters a
magnetic field, an electric force is
exerted on it. If a charged particle
moves at an angle to a magnetic field,
the magnetic force acting on it will
cause it to move in a spiral around the
magnetic field lines.
The solar wind is constantly bombarding
the Earth’s magnetic field. Sometimes
these charged particles penetrate that
field. These particles are found in two
large regions known as the Van Allen
Belts.
The Earth’s magnetic field extends far into
space. It is called the “magnetosphere.”
When the magnetic particles from the sun, called “solar
wind”, strike this magnetosphere, we see a phenomenon
called…
The Aurora Borealis in the Northern Hemisphere
And the Aurora Australis in the Southern Hemisphere
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.
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 
Simple as that!!
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.
Carefully study the next diagrams:
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.
Go to this website and click the button for DC then for
AC to visually see the difference between the two.
You can see that the DC source is a battery – current
flows in one direction. The AC source is the generator
and the current alternates once for each revolution.