Download Magnetism - Mr Michael mccloskey

Magnetism
In Magnesia in Ancient
Greece, there lived a
shepherd named
Magnus.
One day, he
was looking
after his sheep
in the hills.
All of a sudden, he felt a mysterious
force pulling his iron staff from his hand.
Even the
iron nails on
his sandals
were being
pulled out.
To his great surprise, he
discovered that it was a huge,
black rock next to him that was
pulling his staff and the nails.
Soon, news spread across the
country about the strange rock
(now called lodestone) that had the
power to pull things to it.
The Greeks later found other similar
black rocks which had this power. These
rocks were named ‘magnets’, after
either Magnesia or Magnus himself.
Magnets today
• Magnets are one of the most important forces in our world
• There is a magnet or an electromagnet inside many things
• Computers store data in magnetic disks and CDs.
• Electromagnets are used to lift heavy objects
• Doctors can see the inside of our bodies
thanks to magnetic resonance imaging (MRI)
• Maglev trains ‘float’ on top of tracks
• The Earth has a magnetic field
which we can use for navigation
What is magnetism?
Magnetism: an
invisible force that
pushes or pulls
magnetic material.
Which materials are
magnetic?
Magnetic Materials
Materials that are attracted to a magnet, but do not
attract or repel each other.
iron nails
steel spoon and knife
Which of the metals below are magnetic metals?
silver (Ag)
A magnetic material is attracted to a magnet.
Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.
Ag
Non-magnetic Materials
Materials that are not attracted to a magnet.
copper container
gold jewelry
…metals such as
gold, aluminium,
silver and copper.
Aluminium
jewelry
All non-metals such as plastic,
wood, paper, glass and clay are
non-magnetic materials.
A magnet has 2 poles
Poles – part of the magnet with
strongest magnetic force.
The poles are called North pole
and South pole
bar magnet
Law of magnets
If you bring 2 bar magnets close together…
Two Opposite poles
attract
Two like poles
repel
If you cut a magnet in half….
you get 2 smaller magnets with 2 poles.
If you cut a magnet into many pieces, each
piece is a magnet with 2 poles.
Inside materials
Materials are made of many tiny
electrons. They are always
spinning around.
Domain - A group of spinning
electrons.
Each domain acts as a tiny
magnet.
In non-magnetic materials, the
domains are pointing in all
directions
Domains inside magnetic materials
In magnetic materials, the
domains are pointing in one
direction.
The domains (tiny magnets)
are working together and
make the entire object
magnetic.
Magnets have magnetic fields
A magnetic field is the area around a magnet
where there is a magnetic force
Magnetic force is invisible, so
how can we draw the magnetic
field lines?
If you put some iron filings around a magnet, you can see
the magnetic field lines.
weakest field further
away from poles
strongest
field at
poles
The direction of the magnetic
force is from NORTH to SOUTH
Two like
poles
repel
Two Opposite
poles attract
The earth has a magnetic field
• Earth’s core has
molten iron and
nickel which is
always spinning
• The spinning core
acts like a magnet
Magnetic north
pole and
geographic north
pole are not at
the same place.
Who can tell me…
1. How could you tell which pole is which on
a magnet you made?
2. Why does the earth have a magnetic
field?
3. In a magnet, where is the magnetic force
the strongest?