MAGNETISM: PRINCIPLES AND HISTORY Magnetism 1 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
Magnetism 2 Abstract Magnetism permeates every aspect of our lives. Man’s curiosity and desire to understandthe world around him has led to significant discoveries throughout history. Magnetism wasbelieved to have been discovered as early as 600 B.C., but even to this day we have yet to fullyunderstand the power and complexity of the magnetic field. We acknowledge our currentunderstanding of magnetics by developing applications to improve our lives, such as computers,transportation, and medical procedures, and energy generation to power them all. As ourunderstanding of magnetism evolves, so too will the ways in which we apply it. The future ofmilitary technology, transportation, computers, and medicine may well lie in the field ofmagnetics. Keywords: Magnetism, magnets, magnetic poles
Magnetism 3 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 simplecompass by suspending a metal rod. Since then, the applications of magnets has progressedtremendously. 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 modernsociety. History600 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 shepherdnamed Magnes. Legend has it that Magnes was herding his sheep in an area of Northern Greececalled Magnesia. Suddenly both, the nails in his shoes and the metal tip of his herding staffbecame firmly stuck to a large, black rock on which he was standing. To find the source ofattraction he dug up the Earth to find lodestones. Lodestones contain magnetite, a naturalmagnetic material Fe3O4 (“historyofmagnets.com”). This type of rock was subsequently namedmagnetite, 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 oflodestone was by the Chinese. In 121 AD the Chinese suspended a magnetized iron rod. Theyfound out that a lodestone would always point in a north-south direction if it was allowed torotate freely. The Chinese developed the mariners compass more than 4000 years ago. The
Magnetism 4earliest mariners 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 thehandle 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 andPliny the Elder. Pliny wrote of a hill near the river Indus that was made entirely of a stone thatattracted iron. He mentioned the magical powers of magnetite in his writings. For many yearsfollowing its discovery, magnetite was surrounded in superstition and was considered to possessmagical powers, such as the ability to heal the sick, frighten away evil spirits and attract anddissolve ships made of iron. People soon realized that magnetite not only attracted objects made of iron, but whenmade into the shape of a needle and floated on water, magnetite always pointed in a north-southdirection creating a primitive compass. This led to an alternative name for magnetite, that oflodestone 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) andthat 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 samekind 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 rationalexplanation to the mysterious ability of the compass needle to point north-south: the Earth itselfwas magnetic. "De Magnete" opened the era of modern physics and astronomy and started acentury marked by the great achievements of Galileo, Kepler, Newton and others.
Magnetism 5 Gilbert recorded three ways to magnetize a steel needle: by touch with a loadstone; bycold drawing in a North-South direction; and by exposure for a long time to the Earths magneticfield while in a North-South orientation.1740: First Commercial Magnet Gowen Knight produces the first artificial magnets for sale to scientific investigators andterrestrial navigators. The magnets were a navigation tool used to determine the position of theship using terrestrial landmarks such as light house, buoys, islands, and other fixed objects. The Principals Behind Magnets and MagnetismTypes of magnetsThere are a variety of magnets, but they usually fall into one of these three categories: permanentmagnets, temporary magnets, and electromagnets. Permanent Magnets/Natural Magnets. Also known as natural magnets, permanentmagnets are a type of magnet that retains its magnetic field after it has been removed fromanother 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 magnetswhile in a magnetic field, although they lose their magnetic property when they leave thatmagnetic field. Electromagnets. Electromagnets are magnets created when you have a wire with anelectric current running through them. Stronger electromagnets are created when the wire iscoiled around a core.Magnetic Properties We make magnets work by utilizing the magnetic poles, forces, fields and the domains of
Magnetism 6the 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 byPaul G. Hewitt: “Like poles repel each other; opposite poles attract” (Hewitt, 2009). The polesalso attract certain elements like iron, steel, and nickel and slightly repel others like water andboron. These poles become pronounced in temporary magnets when the magnetic domainsbecome aligned. When they are aligned they also increase the strength of the magnetic fieldsurrounding the magnet. Fields. A magnetic field surrounds a magnet, the field itself is created by relative motionof 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 strongmagnetic force.. In unmagnetized iron, the domains are random. In a strong magnet, the domainsnorth and south poles are all lined up. Figure 2 demonstrates how the relationship betweendomains of an object, what happens when they are lined up, and the stronger the magnetic fieldgets.(The red arrow represents the strength of the magnetic field).
Magnetism 7 Figure 2 (Hoadley, 1998) Magnetic domains relative to the strength of a magnetElectricity and Magnetism Electromagnets. Electromagnets are created when a when a wire is coiled and electriccurrent is running through the wire. The electromagnet becomes much stronger if it has a core, ofiron 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 magneticfield it gets deflected, When a moving charge in a wire gets deflected, it can cause the wire, todistort according to the power of the magnet, and the polarity of both the magnet and the currentflowing through the wireElectric and Magnetic calculations The fun stuff, or rather the more complicated stuff that physicists use to make theirevaluations and observations.Interaction between magnetic poles. The force of interaction between 2 poles is calculated bythis first equation in Table 1. The second equation, Coloumbs law, is very similar and used to
Magnetism 8describe “the relationships between electrical force, charge, and distance.(Hewitt, 2009)” p1p2 q1q2 F= -------- F=k---------- d² d² Figure 3: Interaction between 2 poles Coloumbs lawMath 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 displaysMaxwells equations, while table 2 is the key to understanding the equations.
Magnetism 9 Table 1: Maxwells EquationsSymbol Meaning MKS units Gaussian units magnetic induction (tesla) (gauss) velocity of light (meters per second) (centimeters per second) electric displacement (newtons per coulomb) (dynes per statcoulomb) electric field strength (newtons per coulomb) (dynes per statcoulomb) force (newton) (dyne) magnetic field intensity (amperes per meter) (gauss) current density (amperes per square (gauss per meter) meter) magnetization (amperes per meter) (gauss) charge (coulomb) (statcoulomb) (coulomb per cubic (statcoulomb per cubic volume charge density meter) centimeter) velocity (meters per second) (centimeters per second)Table 2: Defining Maxwells equations
Magnetism 10 Commercial Use of Magnets The use of magnets in modern society is vast. From simple refrigerator magnets tocomputer hard drives, magnets are very prevalent in our daily lives. Magnets are found intelevisions, credit cards, speakers and computers. Maglev trains use the force of magnets topropel trains over 300 miles per hour. Magnets are also used in the medical field and inalternative energy.Electromagnets and Modern Technology Computer hard drives. Magnetism plays an important role in the technologicaladvancements in our society. Computer hard drives, for example, use magnets to store and readinformation. Hard drives store information on magnetic disks called platters and useelectromagnets to read or write information. The electromagnet in a read/write head leavesinformation on the hard drive by sending electrical impulses that leave positive or negativemagnetic polarities on the platter disk. These magnetic charges translate into 1s or 0s that arelater read by the read/write head (Museum of Science). Figure 6 shows a read/write headencoding information onto a platter.
Magnetism 11 Figure 6: Platter disk and read/write head Television screens. Before the invention of plasma and LCD screens, magnets were usedin CRT television screens. Inside the television, electrons are shot at the back of the screen whichis covered with phosphor that lights up when excited by the electrons. Magnetic fields within thetelevision are used to guide the electrons to particular parts of the screen and to hit certain spotsof colored phosphor. This produces a full sized and colorful image, rather than a spot on thescreen (Marshall 2012). If a powerful magnet is placed by a CRT television, the magnet field isdisturbed and the image on the screen becomes distorted. Speakers. Magnets are also used in the function of speakers. A permanent magnet isplaced behind the coil of an electromagnet. The polarity of the electromagnet changes rapidlycausing the coil be repelled or attracted to the permanent magnet which results in a vibration. Acone surrounding the vibrating electromagnet amplifies the vibrations and guides the soundwaves out of the speaker (Institute of Physics). The vibrations frequency determines the pitch ofthe sound and the amplitude affects the volume. If the volume of speakers is turned all the wayup, 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 usemagnets to store information. The magnetic strip, often called a magstripe, is made out of ironoxide particles which are needle shaped and easily oriented in particular directions by devicesthat excerpt a strong magnetic force over a small area. The iron fillings can be oriented to have anorth pole or south pole which encodes information onto the magstripe (Association). If a strongmagnet is placed next to a magstripe, the iron particles will be rearranged an the information islost.
Magnetism 12Maglev (Magnet Levitation) Mechanism. Maglev trains (short for magnetic levitation) are powerful trains powered bymagnets. The Maglev train track, also called the guideway, is lined with electromagnetic coilsthat push against magnets on the underside of the train. The opposite polarities on the train andguideway allow the Maglev train to levitate 1 to 10 cm above the guideway. Once the train islevitating, the electromagnet coils on the sides of the guideway alternate their polarities to propelthe train forward. The magnets in front of the train attract the magnets on the train pulling itforward. Meanwhile the magnets behind the train repel the magnets on the train which pushes thetrain 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 withthe lack of friction (because the train is levitating), the trains sleek aerodynamic design, and thepower of magnets. Shanghai Transrapid Line. The first Maglev train was built and tested in Shanghi, Chinain 2002 and still runs today. This Maglev train is called the Shanghi Transrapid line. The 19 mileShanghi Transrapid line travels 276 miles per hour. A trip on the Shanghi Transrapid line travels19 miles in 10 minutes. The same trip would take an hour in a taxi. By 2010, nearly 100 mileswill 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 timeefficient. The environmental impact Maglev trains have is much less than other traditional modesof transportation. Maglev trains run on electricity, so there is no carbon dioxide emissions. Inaddition to being energy efficient, Maglev trains require less maintenance than other means oftransportation. Maglevs do not have engines the way motor vehicles do, and parts on a Maglev
Magnetism 13train 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 incrediblyquite which is advantageous to surrounding communities. Constructing Maglev guideways is anincredibly expensive process, but once the train is installed and built, it is cheaper to run thanairplanes, cars, and traditional trains (Powell, Gordon 2005). Image 7 shows the ShanghiTransrapid line. Figure 7: Maglev Train The advantages of Maglev trains has influenced many countries to invest in futureprojects. Cities in Japan, Germany, the United States and many other countries have expressedplans 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 detectcancer, tumors, torn ligaments, multiple sclerosis and other anomalies within the body. MRImachines are enormous tubes that patient enter while laying down on their back. A large, circularsuperconducting magnet lines the tube that patients enter. The gauss is a common unit ofmeasurement used to measure the strength of a magnet. The magnet in a typical MRI scannercreates a field of 5,000 to 20,000 gauss. To put into perspective how strong MRI magnets are,note that the Earths magnetic field is 0.5 gauss (Gould).
Magnetism 14 The large magnet in a MRI scanner aligns hydrogen atoms in the body, which are usuallyspinning, parallel to the magnetic field. Nearly half of the hydrogen atoms are directed north, andnearly half a directed south; these atoms cancel each other out. There are a few remaininghydrogen atoms that are not canceled with an opposing faced atom. These remaining atoms areexcited when radio frequencies are sent through the body. The energy released by the excitedatoms 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 everchanging field where advances are limited seemingly only by what we can imagine. As ourunderstanding of magnets and magnetic fields evolves the number of fields where magnetics canbe applied expands too. Some of the fields where magnetics are on the cusp of implementationare in the environmental field, military applications, the medical field, and in the field ofinformation and technology. These fields will each be explored and the applications that areapplicable to them described in some detail.Environmental application: magnetic detergents Every day we hear about the great and often times detrimental impact various industrieshave on our environment. On April 20, 2010 at 9:45 PM local time an explosion occurredonboard the Deepwater Horizon deep sea drilling rig owned by Transocean and BP. Thisexplosion and the subsequent sinking of the Deepwater Horizon rig, are what led to what is nowthe largest ever oil spill in history. The spill continued for 87 days with oil gushing into the oceanat an estimated rate of 62,000 barrels of oil per day, eventually tapering off to an estimated53,000 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
Magnetism 15the ocean, leaving 4.1 million barrels that did (“On Scene Coordinator,” 2011). The reason thatthis oil spill is being referenced is as such. The impact that this spill had on the environment wascatastrophic, from killing or contaminating marine life, to destroying vegetation both in theocean and on the hundreds of miles of coastlines where the oil eventually washed ashore. Theeffects will still be felt years from now, as efforts are continuously made to clean up stray anddissolved oil. Detergents have been an effective tool in fighting against oil spills for years. Theproblem is that the detergents leave behind harmful byproducts that until now have not been ableto be fully removed from the environment. By adding iron to the molecular makeup of thedetergents, it has given them a magnetic quality which allows them to be manipulated bymagnetic fields (Brown, et al., 2012). This would not only make it possible to control the spreadand cleanup of oil spills, but it would also make it possible to reuse and recycle the detergentresulting in much less waste.Military Application: Railgun Almost everyone has heard of a rail gun. It is projectile device which requires nogunpowder. It instead uses electric currents to induce electromagnetic fields which create a forcethat can launch a projectile at much greater velocities than standard weapons which usegunpowder. The force that causes the projectile to fire is described by Lorentz Force Law. Insimplest terms Lorentz Force Law, states that the sum of the forces that act upon a charge includeboth a magnetic force as well as an electric force (Hughes, 2005). What this means is that as thecurrent travels up one rail, across the projectile, and back down the opposing pole, it createsmagnetic fields in both rails and also in the projectile. The flow of current in each of the rails issuch that the fields flow in the same direction between the rails. The projectile has currentflowing through it producing a magnetic field which interacts with the combined field from the
Magnetism 16rails inducing a force on the projectile. The projectile travels along the rails at a rateproportionate to the supplied current minus the drag caused by wind and friction. Although railguns 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 ofcurrent to generate the required magnetic fields for propelling the projectile. The secondproblem 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 ofthe metals used to construct the rails that conduct the electricity and guide the projectile in itspath. It’s the same principle as with firearms. If the barrel gets too hot, the gun won’t shootstraight, and if it gets excessively hot it would deform the barrel to the extent that it would makethe weapon unsafe to fire. The rails in a rail gun are effectively the barrel of the gun. Figure 8shows the mechanisms of a railgun. Figure 8: Rail GunMedical Application: Antimagnet Shielding Another development that has potential as either a military or a medical application is anew 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 alayer of isotropic magnetic material (Sanchez, Navau, Prat-Camps, & Chen 2011). An isotropic
Magnetism 17magnetic material is a material that contains one or more rare earth metals, comprising up to onethird of its weight. This new antimagnet as it is called is designed to shield a magnetic fieldinside 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 itapplies 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 frommagnetic mines, an antimagnet could shield a pacemaker or a cochlear implant inside of anpatient so that they can receive medical tests that they might otherwise be excluded from, such asMagnetic Resonance Imaging (MRI).Information and technology: heat controlled magnetic storage Computers have come a long way since they were invented. Where once a singlecomputer could fill multiple floors of an office building, it now fit in the palm of a hand. Where acomputer program was once stored on long sequences of punch cards, it can now fit on amicrochip the size of a fingernail or smaller. Even music and media have evolved thanks tomagnetism and the advent of microchips and microprocessors. It once took hours to downloadfiles, where now it takes only seconds or minutes. Technology has increased by leaps andbounds in the last 25 years. No matter how fast technology gets, it still doesn’t hold a candle tothe processing power of the human brain. Imagine if it could though. Imagine if a computercould rival the human brain. Well that may just be what a group of international researchers ledby the University of York’s, Department of Physics have discovered. They have shown that heatcan create the same effects that a magnetic field can in terms of storing data. They have shownthat tiny bursts of heat can cause changes in magnetization. In laymen’s terms, heat can be usedto change the polarity of a portion of storage media. Heat can be used to program the 1’s and 0’s
Magnetism 18into 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 beoverstated. 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 awhole new world of opportunity for discovery. Conclusion Today scientist are examining how the phenomenon of magnetism has made a greatcontribution to the technological revolution. Throughout the years human kind has discoveredthe principle physics, commercial application and properties of magnetism and how theseproperties of magnetism permeate everything on Earth. Extensive research and development inthe field has deepened our understanding of magnetic science and today humankind is betterequipped than ever before to harness the power of magnetism. The application of magnetism is
Magnetism 19diverse and extends to almost all fields of science right from critical medical diagnosis to spaceengineering and information technology.
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