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 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 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 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 Magnetism 4 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. Magnetism 5 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 Magnetism 6 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). Magnetism 7 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 Magnetism 8 describe “the relationships between electrical force, charge, and distance.(Hewitt, 2009)” p1p2 q1q2 F= -------- F=k---------- d² d² Figure 3: Interaction between 2 poles 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.