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MAGNETISM: PRINCIPLES AND HISTORY
Magnetism
Magnetism: Principles, History, Modern Applications and Future Speculations
Jorey Dixon
Ashley Hyde
Aliza Jensen
Clint Wilkinson
Salt Lake Community College, Physics Department, PHYSCSC 1010, Elementary Physics
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Abstract
Magnetism permeates every aspect of our lives. Man’s curiosity and desire to understand
the world around him has led to significant discoveries throughout history. Magnetism was
believed to have been discovered as early as 600 B.C., but even to this day we have yet to fully
understand the power and complexity of the magnetic field. We acknowledge our current
understanding of magnetics by developing applications to improve our lives, such as computers,
transportation, and medical procedures, and energy generation to power them all. As our
understanding of magnetism evolves, so too will the ways in which we apply it. The future of
military technology, transportation, computers, and medicine may well lie in the field of
magnetics.
Keywords: Magnetism, magnets, magnetic poles
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Magnetism: Principals, History, Modern Applications and Future Speculations
Introduction
One of the earliest uses of magnets was in 121 AD when the Chinese designed a simple
compass by suspending a metal rod. Since then, the applications of magnets has progressed
tremendously. Magnets are currently on the front line of modern technology and as time goes by,
it is apparent that magnets have the potential to power some of the greatest tools of modern
society.
History
600 b.c: Lodestone
The history of magnetism started in the early 600 BC with the discovery of loadstone.
The most popular legend accounting for the discovery of magnets is that of an elderly shepherd
named Magnes. Legend has it that Magnes was herding his sheep in an area of Northern Greece
called Magnesia. Suddenly both, the nails in his shoes and the metal tip of his herding staff
became firmly stuck to a large, black rock on which he was standing. To find the source of
attraction he dug up the Earth to find lodestones. Lodestones contain magnetite, a natural
magnetic material Fe3O4 (“historyofmagnets.com”). This type of rock was subsequently named
magnetite, after either Magnesia or Magnes the shepherd himself.
121 a.d: First Reference to a compass
In 121 AD the first reference to a compass was the earliest discovery of the properties of
lodestone was by the Chinese. In 121 AD the Chinese suspended a magnetized iron rod. They
found out that a lodestone would always point in a north-south direction if it was allowed to
rotate freely. The Chinese developed the mariner's compass more than 4000 years ago. The
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earliest mariner's compass consists of a spoon-shaped magnetite object with a smooth bottom,
set on a polished copper surface. When pushed it rotated freely and usually came to rest with the
handle pointing South. The rod pointed to the magnetic north and south poles.
Stories of magnetism date back to the first century B.C in the writings of Lucretius and
Pliny the Elder. Pliny wrote of a hill near the river Indus that was made entirely of a stone that
attracted iron. He mentioned the magical powers of magnetite in his writings. For many years
following its discovery, magnetite was surrounded in superstition and was considered to possess
magical powers, such as the ability to heal the sick, frighten away evil spirits and attract and
dissolve ships made of iron.
People soon realized that magnetite not only attracted objects made of iron, but when
made into the shape of a needle and floated on water, magnetite always pointed in a north-south
direction creating a primitive compass. This led to an alternative name for magnetite, that of
lodestone or "leading stone" (historyofmagnets.com).
1600: Static Electricity- De Magnete
In the 16th century, William Gilbert(1544-1603), the Court Physician to Queen Elizabeth,
proved that many other substances are electric (from the Greek word for amber, elektron) and
that they have two electrical effects. When rubbed with fur, amber acquires resinous electricity;
glass, however, when rubbed with silk, acquires vitreous electricity. Electricity repels the same
kind and attracts the opposite kind of electricity ( Dewitt. G, Paul, Conceptual Physics, pg. 425).
Gilbert also studied magnetism and in 1600 wrote "De Magnete" which gave the first rational
explanation to the mysterious ability of the compass needle to point north-south: the Earth itself
was magnetic. "De Magnete" opened the era of modern physics and astronomy and started a
century marked by the great achievements of Galileo, Kepler, Newton and others.
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Gilbert recorded three ways to magnetize a steel needle: by touch with a loadstone; by
cold drawing in a North-South direction; and by exposure for a long time to the Earth's magnetic
field while in a North-South orientation.
1740: First Commercial Magnet
Gowen Knight produces the first artificial magnets for sale to scientific investigators and
terrestrial navigators. The magnets were a navigation tool used to determine the position of the
ship using terrestrial landmarks such as light house, buoys, islands, and other fixed objects.
The Principals Behind Magnets and Magnetism
Types of magnets
There are a variety of magnets, but they usually fall into one of these three categories: permanent
magnets, temporary magnets, and electromagnets.
Permanent Magnets/Natural Magnets. Also known as natural magnets, permanent
magnets are a type of magnet that retains its magnetic field after it has been removed from
another magnetic field. “There are 4 classes of permanent magnets, Neodymium Iron Boron,
Samarium Cobalt, Alnico, and Ceramic or Ferrite. (Hoadley, 1998)”
Temporary Magnets. Temporary magnets are materials that act like permanent magnets
while in a magnetic field, although they lose their magnetic property when they leave that
magnetic field.
Electromagnets. Electromagnets are magnets created when you have a wire with an
electric current running through them. Stronger electromagnets are created when the wire is
coiled around a core.
Magnetic Properties
We make magnets work by utilizing the magnetic poles, forces, fields and the domains of
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the magnet, by manipulating these, we can make magnets to do all sorts of things.
Poles. Magnets have poles, a north and a south, these poles have properties described by
Paul G. Hewitt: “Like poles repel each other; opposite poles attract” (Hewitt, 2009). The poles
also attract certain elements like iron, steel, and nickel and slightly repel others like water and
boron. These poles become pronounced in temporary magnets when the magnetic domains
become aligned. When they are aligned they also increase the strength of the magnetic field
surrounding the magnet.
Fields. A magnetic field surrounds a magnet, the field itself is created by relative motion
of the electronic charge passing through the object. Electric and magnetic fields are very similar,
and work in tandem with each other. Figure 1 shows an example of a magnetic field.
Figure 1: Magnetic Field
Domains. A magnetic domain is an area of an object that has lined up due to a strong
magnetic force.. In unmagnetized iron, the domains are random. In a strong magnet, the domain's
north and south poles are all lined up. Figure 2 demonstrates how the relationship between
domains of an object, what happens when they are lined up, and the stronger the magnetic field
gets.(The red arrow represents the strength of the magnetic field).
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Figure 2 (Hoadley, 1998) Magnetic domains relative to the strength of a magnet
Electricity and Magnetism
Electromagnets. Electromagnets are created when a when a wire is coiled and electric
current is running through the wire. The electromagnet becomes much stronger if it has a core, of
iron or some other material. It can however reach a limit to its strength, as quoted here:
“As the current flowing around the core increases, the number of aligned atoms
increases and the stronger the magnetic field becomes. At least, up to a point.
Sooner or later, all of the atoms that can be aligned will be aligned. At this point,
the magnet is said to be saturated and increasing the electric current flowing
around the core no longer affects the magnetization of the core itself.(Gagnon,
2012)”
Electric fields and magnetic fields. When a moving electric charge passes through a a magnetic
field it gets deflected, When a moving charge in a wire gets deflected, it can cause the wire, to
distort according to the power of the magnet, and the polarity of both the magnet and the current
flowing through the wire
Electric and Magnetic calculations
The fun stuff, or rather the more complicated stuff that physicists use to make their
evaluations and observations.
Interaction between magnetic poles. The force of interaction between 2 poles is calculated by
this first equation in Table 1. The second equation, Coloumbs law, is very similar and used to
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describe “the relationships between electrical force, charge, and distance.(Hewitt, 2009)”
p1p2
F= -------d²
Figure 3: Interaction between 2 poles
q1q2
F=k---------d²
Coloumbs law
Math and terms. This was best explained by Rick Hoadley:
“In order to create and control magnetic fields in an exact way, we need to
carefully understand how the strength of magnetic fields change depending on
how far away you are from the magnet, what shape the magnet is, or if it is a
solenoid or electromagnet. We also need to understand how various materials
react to magnetic fields. In addition, we need to know what to call different
parameters of magnets and fields and strengths and densities and so forth so we
can intelligently communicate with one another.”
It may sound easy, but the equations look more complicated than they sounds. Table 1 displays
Maxwell's equations, while table 2 is the key to understanding the equations.
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Table 1: Maxwell's Equations
Symbol Meaning
magnetic induction
velocity of light
MKS units
(tesla)
(meters per second)
Gaussian units
(gauss)
(centimeters per second)
electric displacement
(newtons per coulomb) (dynes per statcoulomb)
electric field strength
(newtons per coulomb) (dynes per statcoulomb)
force
(newton)
magnetic field
intensity
current density
(amperes per meter)
(amperes per square
meter)
magnetization
charge
volume charge density
velocity
(amperes per meter)
(coulomb)
(coulomb per cubic
meter)
(meters per second)
Table 2: Defining Maxwell's equations
(dyne)
(gauss)
(gauss per meter)
(gauss)
(statcoulomb)
(statcoulomb per cubic
centimeter)
(centimeters per second)
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Commercial Use of Magnets
The use of magnets in modern society is vast. From simple refrigerator magnets to
computer hard drives, magnets are very prevalent in our daily lives. Magnets are found in
televisions, credit cards, speakers and computers. Maglev trains use the force of magnets to
propel trains over 300 miles per hour. Magnets are also used in the medical field and in
alternative energy.
Electromagnets and Modern Technology
Computer hard drives. Magnetism plays an important role in the technological
advancements in our society. Computer hard drives, for example, use magnets to store and read
information. Hard drives store information on magnetic disks called platters and use
electromagnets to read or write information. The electromagnet in a read/write head leaves
information on the hard drive by sending electrical impulses that leave positive or negative
magnetic polarities on the platter disk. These magnetic charges translate into 1's or 0's that are
later read by the read/write head (Museum of Science). Figure 6 shows a read/write head
encoding information onto a platter.
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Figure 6: Platter disk and read/write head
Television screens. Before the invention of plasma and LCD screens, magnets were used
in CRT television screens. Inside the television, electrons are shot at the back of the screen which
is covered with phosphor that lights up when excited by the electrons. Magnetic fields within the
television are used to guide the electrons to particular parts of the screen and to hit certain spots
of colored phosphor. This produces a full sized and colorful image, rather than a spot on the
screen (Marshall 2012). If a powerful magnet is placed by a CRT television, the magnet field is
disturbed and the image on the screen becomes distorted.
Speakers. Magnets are also used in the function of speakers. A permanent magnet is
placed behind the coil of an electromagnet. The polarity of the electromagnet changes rapidly
causing the coil be repelled or attracted to the permanent magnet which results in a vibration. A
cone surrounding the vibrating electromagnet amplifies the vibrations and guides the sound
waves out of the speaker (Institute of Physics). The vibrations frequency determines the pitch of
the sound and the amplitude affects the volume. If the volume of speakers is turned all the way
up, the vibrations of the electromagnet can be seen by noticing the pulsating cone covering.
Magstripes. The black strips on the back of credit cards, debit cards, and ATM cards use
magnets to store information. The magnetic strip, often called a magstripe, is made out of iron
oxide particles which are needle shaped and easily oriented in particular directions by devices
that excerpt a strong magnetic force over a small area. The iron fillings can be oriented to have a
north pole or south pole which encodes information onto the magstripe (Association). If a strong
magnet is placed next to a magstripe, the iron particles will be rearranged an the information is
lost.
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Maglev (Magnet Levitation)
Mechanism. Maglev trains (short for magnetic levitation) are powerful trains powered by
magnets. The Maglev train track, also called the guideway, is lined with electromagnetic coils
that push against magnets on the underside of the train. The opposite polarities on the train and
guideway allow the Maglev train to levitate 1 to 10 cm above the guideway. Once the train is
levitating, the electromagnet coils on the sides of the guideway alternate their polarities to propel
the train forward. The magnets in front of the train attract the magnets on the train pulling it
forward. Meanwhile the magnets behind the train repel the magnets on the train which pushes the
train forward (Powell, Gordon 2005). Maglev trains can reach speeds over 300 miles per hour,
over half as fast as the fastest commercial airplane. The trains high speeds has much to do with
the lack of friction (because the train is levitating), the trains sleek aerodynamic design, and the
power of magnets.
Shanghai Transrapid Line. The first Maglev train was built and tested in Shanghi, China
in 2002 and still runs today. This Maglev train is called the Shanghi Transrapid line. The 19 mile
Shanghi Transrapid line travels 276 miles per hour. A trip on the Shanghi Transrapid line travels
19 miles in 10 minutes. The same trip would take an hour in a taxi. By 2010, nearly 100 miles
will be added to the Sanghi Transrapid line, making it the first Maglev line to connect two cities
(Powell, Gordon 2005).
Benefits and future plans. Maglev trains have many benefits aside from being time
efficient. The environmental impact Maglev trains have is much less than other traditional modes
of transportation. Maglev trains run on electricity, so there is no carbon dioxide emissions. In
addition to being energy efficient, Maglev trains require less maintenance than other means of
transportation. Maglevs do not have engines the way motor vehicles do, and parts on a Maglev
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train last longer and have less wear because they are hardly, if ever, in contact with the ground.
Overall, Maglevs are more durable and last longer. Furthermore, Maglev trains are incredibly
quite which is advantageous to surrounding communities. Constructing Maglev guideways is an
incredibly expensive process, but once the train is installed and built, it is cheaper to run than
airplanes, cars, and traditional trains (Powell, Gordon 2005). Image 7 shows the Shanghi
Transrapid line.
Figure 7: Maglev Train
The advantages of Maglev trains has influenced many countries to invest in future
projects. Cities in Japan, Germany, the United States and many other countries have expressed
plans for future Maglev trains.
Medical uses: MRI scanners
Magnets play an important role in the medical field. Magnetic resonance imaging (MRI)
scanners are machines used to create images of the human body. MRI scanners are used to detect
cancer, tumors, torn ligaments, multiple sclerosis and other anomalies within the body. MRI
machines are enormous tubes that patient enter while laying down on their back. A large, circular
superconducting magnet lines the tube that patients enter. The gauss is a common unit of
measurement used to measure the strength of a magnet. The magnet in a typical MRI scanner
creates a field of 5,000 to 20,000 gauss. To put into perspective how strong MRI magnets are,
note that the Earth's magnetic field is 0.5 gauss (Gould).
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The large magnet in a MRI scanner aligns hydrogen atoms in the body, which are usually
spinning, parallel to the magnetic field. Nearly half of the hydrogen atoms are directed north, and
nearly half a directed south; these atoms cancel each other out. There are a few remaining
hydrogen atoms that are not canceled with an opposing faced atom. These remaining atoms are
excited when radio frequencies are sent through the body. The energy released by the excited
atoms is sent to a computer that uses the information to create an image (Gould).
Future Speculations And Applications
Although there are already many commercial uses for magnets, magnetics is an ever
changing field where advances are limited seemingly only by what we can imagine. As our
understanding of magnets and magnetic fields evolves the number of fields where magnetics can
be applied expands too. Some of the fields where magnetics are on the cusp of implementation
are in the environmental field, military applications, the medical field, and in the field of
information and technology. These fields will each be explored and the applications that are
applicable to them described in some detail.
Environmental application: magnetic detergents
Every day we hear about the great and often times detrimental impact various industries
have on our environment. On April 20, 2010 at 9:45 PM local time an explosion occurred
onboard the Deepwater Horizon deep sea drilling rig owned by Transocean and BP. This
explosion and the subsequent sinking of the Deepwater Horizon rig, are what led to what is now
the largest ever oil spill in history. The spill continued for 87 days with oil gushing into the ocean
at an estimated rate of 62,000 barrels of oil per day, eventually tapering off to an estimated
53,000 barrels per day. The total amount of oil that escaped the well was 4.9 million barrels
(205.8 million gallons). BP was only able to capture 800,000 barrels of oil that never touched
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the ocean, leaving 4.1 million barrels that did (“On Scene Coordinator,” 2011). The reason that
this oil spill is being referenced is as such. The impact that this spill had on the environment was
catastrophic, from killing or contaminating marine life, to destroying vegetation both in the
ocean and on the hundreds of miles of coastlines where the oil eventually washed ashore. The
effects will still be felt years from now, as efforts are continuously made to clean up stray and
dissolved oil. Detergents have been an effective tool in fighting against oil spills for years. The
problem is that the detergents leave behind harmful byproducts that until now have not been able
to be fully removed from the environment. By adding iron to the molecular makeup of the
detergents, it has given them a magnetic quality which allows them to be manipulated by
magnetic fields (Brown, et al., 2012). This would not only make it possible to control the spread
and cleanup of oil spills, but it would also make it possible to reuse and recycle the detergent
resulting in much less waste.
Military Application: Railgun
Almost everyone has heard of a rail gun. It is projectile device which requires no
gunpowder. It instead uses electric currents to induce electromagnetic fields which create a force
that can launch a projectile at much greater velocities than standard weapons which use
gunpowder. The force that causes the projectile to fire is described by Lorentz Force Law. In
simplest terms Lorentz Force Law, states that the sum of the forces that act upon a charge include
both a magnetic force as well as an electric force (Hughes, 2005). What this means is that as the
current travels up one rail, across the projectile, and back down the opposing pole, it creates
magnetic fields in both rails and also in the projectile. The flow of current in each of the rails is
such that the fields flow in the same direction between the rails. The projectile has current
flowing through it producing a magnetic field which interacts with the combined field from the
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rails inducing a force on the projectile. The projectile travels along the rails at a rate
proportionate to the supplied current minus the drag caused by wind and friction. Although rail
guns have been built and tested since the 1980’s, a practical use has yet to be found for them.
There are two main problems with rail guns. The first is that they require an excessive amount of
current to generate the required magnetic fields for propelling the projectile. The second
problem is linked to the first. Enormous amounts of current generate enormous amounts of heat.
Heat is a problem because in sufficient quantities, it will cause deformation and degradation of
the metals used to construct the rails that conduct the electricity and guide the projectile in its
path. It’s the same principle as with firearms. If the barrel gets too hot, the gun won’t shoot
straight, and if it gets excessively hot it would deform the barrel to the extent that it would make
the weapon unsafe to fire. The rails in a rail gun are effectively the barrel of the gun. Figure 8
shows the mechanisms of a railgun.
Figure 8:
Rail Gun
Medical Application: Antimagnet Shielding
Another development that has potential as either a military or a medical application is a
new theoretical material being called an anitmagnet. It is actually a combination of materials.
On the inside would be a layer of superconductor material and on the outermost layer would be a
layer of isotropic magnetic material (Sanchez, Navau, Prat-Camps, & Chen 2011). An isotropic
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magnetic material is a material that contains one or more rare earth metals, comprising up to one
third of its weight. This new antimagnet as it is called is designed to shield a magnetic field
inside of it from all outside magnetic field. So effectively magnetic fields can’t escape from it,
and outside magnetic fields do not affect it at all. The importance of this is two-fold. First, as it
applies to the military, we can shield our ships and various other vehicles from magnetic mines,
both in the water and on land. In addition to shielding our military from potential threats from
magnetic mines, an antimagnet could shield a pacemaker or a cochlear implant inside of an
patient so that they can receive medical tests that they might otherwise be excluded from, such as
Magnetic Resonance Imaging (MRI).
Information and technology: heat controlled magnetic storage
Computers have come a long way since they were invented. Where once a single
computer could fill multiple floors of an office building, it now fit in the palm of a hand. Where a
computer program was once stored on long sequences of punch cards, it can now fit on a
microchip the size of a fingernail or smaller. Even music and media have evolved thanks to
magnetism and the advent of microchips and microprocessors. It once took hours to download
files, where now it takes only seconds or minutes. Technology has increased by leaps and
bounds in the last 25 years. No matter how fast technology gets, it still doesn’t hold a candle to
the processing power of the human brain. Imagine if it could though. Imagine if a computer
could rival the human brain. Well that may just be what a group of international researchers led
by the University of York’s, Department of Physics have discovered. They have shown that heat
can create the same effects that a magnetic field can in terms of storing data. They have shown
that tiny bursts of heat can cause changes in magnetization. In laymen’s terms, heat can be used
to change the polarity of a portion of storage media. Heat can be used to program the 1’s and 0’s
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into your computer which make up computer programs without the need for a magnetic field.
The significance of being able to write a program without the use of a magnetic field cannot be
overstated. The following is excerpt from an article for the University of York, News and Events:
York physicist Thomas Ostler said: "Instead of using a magnetic field to record
information on a magnetic medium, we harnessed much stronger internal forces
and recorded information using only heat. This revolutionary method allows the
recording of Terabytes (thousands of Gigabytes) of information per second,
hundreds of times faster than present hard drive technology. As there is no need
for a magnetic field, there is also less energy consumption." (“Scientists record,”
2012, 3).
With the potential of such computing speeds nearing reality, the door is open to a
whole new world of opportunity for discovery.
Conclusion
Today scientist are examining how the phenomenon of magnetism has made a great
contribution to the technological revolution. Throughout the years human kind has discovered
the principle physics, commercial application and properties of magnetism and how these
properties of magnetism permeate everything on Earth. Extensive research and development in
the field has deepened our understanding of magnetic science and today humankind is better
equipped than ever before to harness the power of magnetism. The application of magnetism is
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diverse and extends to almost all fields of science right from critical medical diagnosis to space
engineering and information technology.
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