Download Magnetism Leaflet

Magnetism
KEY POINTS:
1.Magnets are strongest at the poles
2.The poles are North and South
3.Iron, Nickel and Cobalt are magnetic elements
(steel is also magnetic, but is an alloy)
Magnetic Resonance Imaging Scan
4.There is an invisible magnetic field around the
magnet, which exerts a force on the magnetic materials
mentioned in (3.)
HISTORY

This magnetic resonance imaging (MRI) scan
through a normal adult head shows the brain,
airways, and soft tissues of the face. MRI has
become a valuable diagnostic tool, and is especially
effective at imaging these areas of the body.
ADVANCED
The ancient Greeks, Romans and Chinese knew of
Lodestone (now called Magnetite) was a type of
Iron ore
Magnetic materials can be classified as:

The first compass was used about AD 1200

1. Diamagnetic- when placed in a magnetic field they
have a moment induced which opposes the direction
of the magnetic field
The English physicist and doctor William Gilbert
published his book Of Magnets, Magnetic
Bodies, and the Great Magnet of the Earth in
1600. Gilbert applied scientific methods to the study
of electricity and magnetism. He pointed out that
the Earth itself behaves like a giant magnet

In 1750, the English geologist John Michell
invented a balance that he used in the study of
magnetic forces. He showed that the attraction or
repulsion between two magnetic poles decreases as
the square of the distance between them increases
2. Paramagnetic- in a magnetic field the moments
add to the magnetic field
3. Ferromagnetic- retains a magnetic force even
when there is no external magnetic field.
The Curie temperature for Iron is 770°C, it loses all
magnetic properties
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Earth's Magnetic Field
A powerful magnetic field surrounds the earth,
as if the planet had an enormous bar magnet
embedded in its interior. However,
geophysicists believe that convection currents of
charged, molten metal circulating in the
earth’s core are the source of the magnetic
field. A compass needle is a true bar magnet;
one end of it is called “north-seeking” because
it is attracted to the magnetic pole that lies
within the earth in the northern hemisphere.
The other end of the compass needle is a
magnetic pole of the opposite kind, and is
therefore attracted to the earth’s other magnetic
pole. Since opposite types of magnetic pole
attract each other, the pole in the northern
hemisphere, although called the north magnetic
pole, is itself of the south-seeking type, and
vice versa for the opposite hemisphere.

MAGNETISM
1. Magnets made of steel are “permanent” magnets in
that they can retain their magnetism for a long time
2. Magnets made of soft iron can easily lose their
magnetism, and are called “temporary” magnets, but
this makes them particularly useful in electromagnets
3. When freely suspended a magnet will point to
magnetic North
4. If two magnets are close to one another, their “like”
poles (north-north, etc.) repel one another, and their
"unlike" poles (north-south) attract one another
.MAKING A MAGNET
A piece of iron or steel can become magnetized in
three ways:
1. By stroking it gently, from end to end, with
one pole of an existing magnet
2. By tapping gently while it is lying along a
magnetic field (this is how screwdrivers and other
tools can become accidentally magnetized)
3. By placing it inside a long cylindrical coil of
many turns of wire (a solenoid), and passing a
strong direct current through the coil for a short
period
USES FOR MAGNETS
In computers magnetized ‘bubble domains’
store information
Also done with tapes, videos, CDs, DVDs
and disks
Magnetic levitation trains float above the
tracks using strong magnets, so that there is no
friction with the tracks to slow the trains down
Nuclear Magnetic Resonance Imaging
(MRI) imaging in hospitals
Magnets contain lots of tiny domains (like
tiny magnets), when they are not lined up
the metal is not magnetic
HOW TO DEMAGNETIZE A
MAGNET
A magnet can be demagnetized by:
1. Hitting it repeatedly
2. Placing it in a solenoid and reducing the current
down to zero
3. Heat the magnet
The magnetic field around a bar magnet. The
force point to the South pole and away from
the North pole
HOW TO FIND THE MAGNETIC
FIELD
1.
You can sprinkle Iron filings onto a piece of
paper above the magnet and tap the page. The
filings line up along the magnetic lines of force
2.
Use compasses to plot the lines of force
around the magnet (this allows you to work out
the North and South poles)
Magnetic Levitation Train
Magnetic levitation trains levitate above the track by means of a
magnetic suspension system, thus reducing or eliminating
vibration, friction, and noise. Magnetic levitation trains can
reach extremely high speeds; this experimental train in Germany,
above, reaches 435 km/h (270 mph).