Transcript 1a.Magnetism

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Magnetism
Kyle Thornton
DMI 50B
Lecture Objectives
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Define magnetism
Identify the magnetic properties
Define magnetic moment, magnetic domains
Explain how a magnet is able to exert force
through space
List the three different types of magnets and give
an example of each
Classify different materials with regard to their
magnetic susceptibility
What Is Magnetism?
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The ability of certain metallic substances to attract iron,
cobalt, and nickel
Magnetism was discovered as early as the 6th century, BC
First artificial magnet was discovered in China around 1
AD by stroking certain materials with iron
The first technological application of magnetism is
believed to be the compass
There are many similarities between magnetism and
electricity
Application Of Magnetism In
Radiology
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Used to produce images in Magnetic
Resonance Imaging (MRI)
 Utilizes
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very strong magnetic fields
Used in the circuitry of the X-ray machine
and other x-ray apparatus
Magnetic Properties
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All magnets have two poles
 North
 South
If cut in two - each half will develop north and south pole
Like magnetic poles repel, opposite poles attract
The force of attraction between two magnetic poles is
directly related to the strength of the magnets and inversely
related to the square of the distance between them
Magnetic Lines of Force
http://micro.magnet.fsu.edu/electromag/java
/magneticlines/index.html
 http://micro.magnet.fsu.edu/electromag/java
/magneticlines2/index.html
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More Magnetic Properties
Some materials can be easily magnetized,
others cannot
 Magnetic fields exist around magnets
 The strength of a magnet can be adversely
affected by heating or mechanically jarring
it
 Materials can be magnetized by leaving
them near a strong magnet or stroking them
with another magnet
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Atoms - The Smallest Magnet
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Any charged particle in motion creates a magnetic field
Spinning electric charges such as electrons induce a
magnetic field
Magnetic domains
 A group of atoms
 Each atom behaves like a tiny magnet
 These atoms determine the overall magnetic properties
of the magnet
 Each atom has a north and south pole
Magnetic Domains
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Order of magnetic domains
 Unmagnetized bar
 Domains in random order
 Magnetized bar
 Domains are aligned in the same direction
 This can be accomplished by dragging a strong
magnet over a steel or iron bar
 Domains can be knocked out of alignment by
physical force or heating
 This will destroy a permanent magnet
How Does MRI Work?
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In the nucleus of an atom, a proton spinning
creates a nuclear magnetic dipole
 This
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is called a magnetic moment
The magnetic moments of hydrogen atoms
in the body is the basis for MRI
Magnetic Fields
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A magnet has the ability to exert force over
distance
 This
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is accomplished by magnetic fields
Direction of magnetic fields
 Flow
from north to south outside the magnet
 Flow from south to north inside the magnet
Three Principal Types of Magnets
Naturally Occurring Magnets
 Artificially Induced Permanent Magnets
 Electromagnets
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Unit of Magnetic Strength
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Magnetic Strength
 The
magnitude of magnetic force exerted on an
object
Tesla
 Gauss
 10,000 Gauss = 1 Tesla
 MRI units are generally around 1.5 Tesla
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Classification of Magnetic
Materials
Dimagnetic
 Paramagnetic
 Ferromagnetic
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 High
magnetic susceptibility
Review questions
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What is magnetism?
Name two applications of magnetism in Radiology
What will occur if two magnetic poles that are positive are
brought together?
If the distance between two magnets is doubled, what will
happen to the strength of the magnetic field?
How are the magnetic domains aligned in an object that
has been magnetized?
What is the term for a magnet that has been wrapped in a
coil of wire?
How would the substance gadolinium be classified?