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11.2: Magnetism and Its Historical Discoveries

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Learning Objectives

By the end of this section, you will be able to:

• Explain attraction and repulsion by magnets
• Describe the historical and contemporary applications of magnetism

Magnetism has been known since the time of the ancient Greeks, but it has always been a bit mysterious. You can see electricity in the flash of a lightning bolt, but when a compass needle points to magnetic north, you can’t see any force causing it to rotate. People learned about magnetic properties gradually, over many years, before several physicists of the nineteenth century connected magnetism with electricity. In this section, we review the basic ideas of magnetism and describe how they fit into the picture of a magnetic field.

Brief History of Magnetism

Magnets are commonly found in everyday objects, such as toys, hangers, elevators, doorbells, and computer devices. Experimentation on these magnets shows that all magnets have two poles: One is labeled north (N) and the other is labeled south (S). Magnetic poles repel if they are alike (both N or both S), they attract if they are opposite (one N and the other S), and both poles of a magnet attract unmagnetized pieces of iron. An important point to note here is that you cannot isolate an individual magnetic pole. Every piece of a magnet, no matter how small, which contains a north pole must also contain a south pole.

Visit this website for an interactive demonstration of magnetic north and south poles.

An example of a magnet is a compass needle . It is simply a thin bar magnet suspended at its center, so it is free to rotate in a horizontal plane. Earth itself also acts like a very large bar magnet, with its south-seeking pole near the geographic North Pole (Figure \(\PageIndex{1}\)). The north pole of a compass is attracted toward Earth’s geographic North Pole because the magnetic pole that is near the geographic North Pole is actually a south magnetic pole. Confusion arises because the geographic term “North Pole” has come to be used (incorrectly) for the magnetic pole that is near the North Pole. Thus, “ north magnetic pole ” is actually a misnomer—it should be called the south magnetic pole . [Note that the orientation of Earth’s magnetic field is not permanent but changes (“flips”) after long time intervals. Eventually, Earth’s north magnetic pole may be located near its geographic North Pole.]

Back in 1819, the Danish physicist Hans Oersted was performing a lecture demonstration for some students and noticed that a compass needle moved whenever current flowed in a nearby wire. Further investigation of this phenomenon convinced Oersted that an electric current could somehow cause a magnetic force. He reported this finding to an 1820 meeting of the French Academy of Science.

Soon after this report, Oersted’s investigations were repeated and expanded upon by other scientists. Among those whose work was especially important were Jean-Baptiste Biot and Felix Savart , who investigated the forces exerted on magnets by currents; André Marie Ampère , who studied the forces exerted by one current on another; François Arago , who found that iron could be magnetized by a current; and Humphry Davy , who discovered that a magnet exerts a force on a wire carrying an electric current. Within 10 years of Oersted’s discovery, Michael Faraday found that the relative motion of a magnet and a metallic wire induced current in the wire. This finding showed not only that a current has a magnetic effect, but that a magnet can generate electric current. You will see later that the names of Biot, Savart, Ampère, and Faraday are linked to some of the fundamental laws of electromagnetism.

The evidence from these various experiments led Ampère to propose that electric current is the source of all magnetic phenomena. To explain permanent magnets, he suggested that matter contains microscopic current loops that are somehow aligned when a material is magnetized. Today, we know that permanent magnets are actually created by the alignment of spinning electrons, a situation quite similar to that proposed by Ampère. This model of permanent magnets was developed by Ampère almost a century before the atomic nature of matter was understood. (For a full quantum mechanical treatment of magnetic spins, see Quantum Mechanics and Atomic Structure .)

Contemporary Applications of Magnetism

Today, magnetism plays many important roles in our lives. Physicists’ understanding of magnetism has enabled the development of technologies that affect both individuals and society. The electronic tablet in your purse or backpack, for example, wouldn’t have been possible without the applications of magnetism and electricity on a small scale (Figure \(\PageIndex{2}\)). Weak changes in a magnetic field in a thin film of iron and chromium were discovered to bring about much larger changes in resistance, called giant magnetoresistance . Information can then be recorded magnetically based on the direction in which the iron layer is magnetized. As a result of the discovery of giant magnetoresistance and its applications to digital storage, the 2007 Nobel Prize in Physics was awarded to Albert Fert from France and Peter Grunberg from Germany.

All electric motors—with uses as diverse as powering refrigerators, starting cars, and moving elevators—contain magnets. Generators, whether producing hydroelectric power or running bicycle lights, use magnetic fields. Recycling facilities employ magnets to separate iron from other refuse. Research into using magnetic containment of fusion as a future energy source has been continuing for several years. Magnetic resonance imaging (MRI) has become an important diagnostic tool in the field of medicine, and the use of magnetism to explore brain activity is a subject of contemporary research and development. The list of applications also includes computer hard drives, tape recording, detection of inhaled asbestos, and levitation of high-speed trains. Magnetism is involved in the structure of atomic energy levels, as well as the motion of cosmic rays and charged particles trapped in the Van Allen belts around Earth. Once again, we see that all these disparate phenomena are linked by a small number of underlying physical principles.

Contributors and Attributions

Samuel J. Ling (Truman State University), Jeff Sanny (Loyola Marymount University), and Bill Moebs with many contributing authors. This work is licensed by OpenStax University Physics under a  Creative Commons Attribution License (by 4.0) .

Magnetism is the force exerted by magnets when they attract or repel each other

Earth Science, Geology, Geography, Geographic Information Systems (GIS)

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Magnetism is the force exerted by magnets when they attract or repel each other. Magnetism is caused by the motion of electric charges . Every substance is made up of tiny units called atoms . Each atom has electrons , particles that carry electric charges . Spinning like tops, the electrons circle the nucleus , or core, of an atom . Their movement generates an electric current and causes each electron to act like a microscopic magnet .

In most substances, equal numbers of electrons spin in opposite directions, which cancels out their magnetism . That is why materials such as cloth or paper are said to be weakly magnetic . In substances such as iron , cobalt , and nickel , most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic —but they are not yet magnets . To become magnetized , another strongly magnetic substance must enter the magnetic field of an existing magnet . The magnetic field is the area around a magnet that has magnetic force . All magnets have north and south poles. Opposite poles are attracted to each other, while the same poles repel each other. When you rub a piece of iron along a magnet , the north-seeking poles of the atoms in the iron line up in the same direction. The force generated by the aligned atoms creates a magnetic field . The piece of iron has become a magnet . Some substances can be magnetized by an electric current . When electricity runs through a coil of wire, it produces a magnetic field . The field around the coil will disappear, however, as soon as the electric current is turned off. Geomagnetic Poles

Earth is a magnet. Scientists do not fully understand why, but they think the movement of molten metal in Earth’s outer core generates electric currents. The currents create a magnetic field with invisible lines of force flowing between Earth’s magnetic poles. The geomagnetic poles are not the same as the North and South Poles. Earth’s magnetic poles often move, due to activity far beneath Earth’s surface. The shifting locations of the geomagnetic poles are recorded in rocks that form when molten material called magma wells up through Earth’s crust and pours out as lava . As lava cools and becomes solid rock, strongly magnetic particles within the rock become magnetized by Earth’s magnetic field. The particles line up along the lines of force in Earth’s field. In this way, rocks lock in a record of the position of Earth’s geomagnetic poles at that time.

Strangely, the magnetic records of rocks formed at the same time seem to point to different locations for the poles. According to the theory of plate tectonics , the rocky plates that make up Earth’s hard shell are constantly moving. Thus, the plates on which the rocks solidified have moved since the rocks recorded the position of the geomagnetic poles. These magnetic records also show that the geomagnetic poles have reversed—changed into the opposite kind of pole—hundreds of times since Earth formed. Earth’s magnetic field does not move quickly or reverse often. Therefore, it can be a useful tool for helping people find their way around. For hundreds of years, people have used magnetic compasses to navigate using Earth’s magnetic field. The magnetic needle of a compass lines up with Earth’s magnetic poles. The north end of a magnet points toward the North Magnetic Pole, which holds a south magnetic charge. Earth’s magnetic field dominates a region called the magnetosphere , which wraps around the planet and its atmosphere . Solar wind , charged particles from the sun, presses the magnetosphere against Earth on the side facing the sun and stretches it into a teardrop shape on the shadow side. The magnetosphere protects Earth from most of the particles, but some leak through it and become trapped. When particles from the solar wind hit atoms of gas in the upper atmosphere around the geomagnetic poles, they produce light displays called auroras . These auroras appear over places like the U.S. state of Alaska, Canada and Scandinavia, where they are sometimes called “ Northern Lights .” The “ Southern Lights ” can be seen in Antarctica and New Zealand.

Animal Magnetism Some animals, such as pigeons, bees, and salmon, can detect Earth's magnetic field and use it to navigate. Scientists aren't sure how they do this, but these creatures seem to have magnetic material in their bodies that acts like a compass.

Historic Directions The ancient Greeks and Chinese knew about naturally magnetic stones called "lodestones." These chunks of iron-rich minerals may have been magnetized by lightning. The Chinese discovered that they could make a needle magnetic by stroking it against a lodestone, and that the needle would point north-south.

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11.1 Magnetism and Its Historical Discoveries

Learning objectives.

By the end of this section, you will be able to:

• Explain attraction and repulsion by magnets
• Describe the historical and contemporary applications of magnetism

Magnetism has been known since the time of the ancient Greeks, but it has always been a bit mysterious. You can see electricity in the flash of a lightning bolt, but when a compass needle points to magnetic north, you can’t see any force causing it to rotate. People learned about magnetic properties gradually, over many years, before several physicists of the nineteenth century connected magnetism with electricity. In this section, we review the basic ideas of magnetism and describe how they fit into the picture of a magnetic field.

Brief History of Magnetism

Magnets are commonly found in everyday objects, such as toys, hangers, elevators, doorbells, and computer devices. Experimentation on these magnets shows that all magnets have two poles: One is labeled north (N) and the other is labeled south (S). Magnetic poles repel if they are alike (both N or both S), they attract if they are opposite (one N and the other S), and both poles of a magnet attract unmagnetized pieces of iron. An important point to note here is that you cannot isolate an individual magnetic pole. Every piece of a magnet, no matter how small, which contains a north pole must also contain a south pole.

Interactive

Visit this website for an interactive demonstration of magnetic north and south poles.

An example of a magnet is a compass needle . It is simply a thin bar magnet suspended at its center, so it is free to rotate in a horizontal plane. Earth itself also acts like a very large bar magnet, with its south-seeking pole near the geographic North Pole ( Figure 11.2 ). The north pole of a compass is attracted toward Earth’s geographic North Pole because the magnetic pole that is near the geographic North Pole is actually a south magnetic pole. Confusion arises because the geographic term “North Pole” has come to be used (incorrectly) for the magnetic pole that is near the North Pole. Thus, “ north magnetic pole ” is actually a misnomer—it should be called the south magnetic pole . [Note that the orientation of Earth’s magnetic field is not permanent but changes (“flips”) after long time intervals. Eventually, Earth’s north magnetic pole may be located near its geographic North Pole.]

Back in 1819, the Danish physicist Hans Oersted was performing a lecture demonstration for some students and noticed that a compass needle moved whenever current flowed in a nearby wire. Further investigation of this phenomenon convinced Oersted that an electric current could somehow cause a magnetic force. He reported this finding to an 1820 meeting of the French Academy of Science.

Soon after this report, Oersted’s investigations were repeated and expanded upon by other scientists. Among those whose work was especially important were Jean-Baptiste Biot and Felix Savart , who investigated the forces exerted on magnets by currents; André Marie Ampère , who studied the forces exerted by one current on another; François Arago , who found that iron could be magnetized by a current; and Humphry Davy , who discovered that a magnet exerts a force on a wire carrying an electric current. Within 10 years of Oersted’s discovery, Michael Faraday found that the relative motion of a magnet and a metallic wire induced current in the wire. This finding showed not only that a current has a magnetic effect, but that a magnet can generate electric current. You will see later that the names of Biot, Savart, Ampère, and Faraday are linked to some of the fundamental laws of electromagnetism.

The evidence from these various experiments led Ampère to propose that electric current is the source of all magnetic phenomena. To explain permanent magnets, he suggested that matter contains microscopic current loops that are somehow aligned when a material is magnetized. Today, we know that permanent magnets are actually created by the alignment of spinning electrons, a situation quite similar to that proposed by Ampère. This model of permanent magnets was developed by Ampère almost a century before the atomic nature of matter was understood. (For a full quantum mechanical treatment of magnetic spins, see Quantum Mechanics and Atomic Structure .)

Contemporary Applications of Magnetism

Today, magnetism plays many important roles in our lives. Physicists’ understanding of magnetism has enabled the development of technologies that affect both individuals and society. The electronic tablet in your purse or backpack, for example, wouldn’t have been possible without the applications of magnetism and electricity on a small scale ( Figure 11.3 ). Weak changes in a magnetic field in a thin film of iron and chromium were discovered to bring about much larger changes in resistance, called giant magnetoresistance . Information can then be recorded magnetically based on the direction in which the iron layer is magnetized. As a result of the discovery of giant magnetoresistance and its applications to digital storage, the 2007 Nobel Prize in Physics was awarded to Albert Fert from France and Peter Grunberg from Germany.

All electric motors—with uses as diverse as powering refrigerators, starting cars, and moving elevators—contain magnets. Generators, whether producing hydroelectric power or running bicycle lights, use magnetic fields. Recycling facilities employ magnets to separate iron from other refuse. Research into using magnetic containment of fusion as a future energy source has been continuing for several years. Magnetic resonance imaging (MRI) has become an important diagnostic tool in the field of medicine, and the use of magnetism to explore brain activity is a subject of contemporary research and development. The list of applications also includes computer hard drives, tape recording, detection of inhaled asbestos, and levitation of high-speed trains. Magnetism is involved in the structure of atomic energy levels, as well as the motion of cosmic rays and charged particles trapped in the Van Allen belts around Earth. Once again, we see that all these disparate phenomena are linked by a small number of underlying physical principles.

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Our timeline guides you through the highlights of electricity and magnetism across the globe and across the centuries.

Grid list page

600 bc - 1599.

Humans discover the magnetic lodestone as well as the attracting properties of amber. Advanced societies, in particular the Chinese and the Europeans,…

1600 - 1699

The Scientific Revolution takes hold, facilitating the groundbreaking work of luminaries such as William Gilbert, who took the first truly scientific …

Aided by tools such as static electricity machines and leyden jars, scientists continue their experiments into the fundamentals of magnetism and elect…

1750 - 1774

With his famous kite experiment and other forays into science, Benjamin Franklin advances knowledge of electricity, inspiring his English friend Josep…

1775 - 1799

Scientists take important steps toward a fuller understanding of electricity, as well as some fruitful missteps, including an elaborate but incorrect …

1800 - 1819

Alessandro Volta invents the first primitive battery, discovering that electricity can be generated through chemical processes; scientists quickly sei…

1820 - 1829

Hans Christian Ørsted’s accidental discovery that an electrical current moves a compass needle rocks the scientific world; a spate of experiments foll…

1830 - 1839

The first telegraphs are constructed and Michael Faraday produces much of his brilliant and enduring research into electricity and magnetism, inventin…

1840 - 1849

The legendary Faraday forges on with his prolific research and the telegraph reaches a milestone when a message is sent between Washington, DC, and Ba…

The Industrial Revolution is in full force, Gramme invents his dynamo and James Clerk Maxwell formulates his series of equations on electrodynamics.

1870 - 1879

The telephone and first practical incandescent light bulb are invented while the word "electron" enters the scientific lexicon.

1880 - 1889

Nikola Tesla and Thomas Edison duke it out over the best way to transmit electricity and Heinrich Hertz is the first person (unbeknownst to him) to br…

1890 - 1899

Scientists discover and probe x-rays and radioactivity, while inventors compete to build the first radio.

1900 - 1909

Albert Einstein publishes his special theory of relativity and his theory on the quantum nature of light, which he identified as both a particle and a…

1910 - 1929

Scientists' understanding of the structure of the atom and of its component particles grows, the phone and radio become common, and the modern televis…

1930 - 1939

New tools such as special microscopes and the cyclotron take research to higher levels, while average citizens enjoy novel amenities such as the FM ra…

1940 - 1959

Defense-related research leads to the computer, the world enters the atomic age and TV conquers America.

1960 - 1979

Computers evolve into PCs, researchers discover one new subatomic particle after another and the space age gives our psyches and science a new context…

1980 - 2003

Scientists explore new energy sources, the World Wide Web spins a vast network and nanotechnology is born.

Electron Timeline

The electron has fascinated humankind for centuries. Here are some highlights from the annals of science.

History of Magnetism

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• Daniel C. Mattis PH. D. 3  

Part of the book series: Springer Series in Solid-State Sciences ((SSSOL,volume 17))

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It was probably the Greeks who first reflected upon the wondrous properties of magnetite, the magnetic iron ore FeO—Fe 2 O 3 and famed lodestone (leading stone, or compass). This mineral, which even in the natural state often has a powerful attraction for iron and steel, was mined in the province of Magnesia.

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Mattis, D.C. (1981). History of Magnetism. In: The Theory of Magnetism I. Springer Series in Solid-State Sciences, vol 17. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-83238-3_1

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• Electricity And Magnetism
• Discovery Magnets

Discovery of Magnets - Applications

History of Magnets:

People from Ancient Egypt started using magnets to play tricks, by making objects of worship float in mid-air by proper positioning of magnets. The emperor from China used magnets to save his palace by constructing gates made of loadstone. The amours made of metal got attracted to the magnetic gates and prevented them from going any further.

In his book, De Magnete (1600), scientist William Gilbert mentioned techniques of artificially making magnets from steel. He used three techniques by which steel can be magnetized permanently:

• Rub the steel needle with a block of loadstone in a particular direction starting from one end and ending at other.
• Forging powdered iron at high temperatures under strong magnetic forces.
• Leaving red-hot iron bars to cool in Earth’s magnetic field for twenty years. This method only had a theoretical basis and was not used for the purpose.

In this video, let’s see what is magnetism and know about a few properties of a magnet

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• Discovery of Magnets

History of Magnets

The history of magnets goes back to 600 B.C. but it was only in the 20th century that scientists began to understand it and the discovery of magnets applications began.

Magnetism was most likely first discovered in a type of magnetite called lodestone, which is made up of iron oxide, a chemical compound made up of iron and oxygen. The first known users of this mineral, which they called a magnet because of its ability to attract other pieces of the same material and iron, were the ancient Greeks.

William Gilbert (1540-1603), an Englishman, was the first to use scientific methods to investigate the phenomenon of magnetism. He also found that the Earth is a weak magnet in and of itself. Carl Friedrich Gauss, a German, conducted the first theoretical studies into the nature of the Earth's magnetism (1777-1855).

The inverse square law of force states that the attractive force between two magnetized objects is directly proportional to the product of their fields and inversely proportional to the square of the distance between them.

Quantitative studies of the history of magnetism and magnetic phenomena began in the 18th century with Frenchman Charles Coulomb (1736-1806), who developed the inverse square law of force, which states that “the attractive force between two magnetized objects is directly proportional to the product of their individual fields and inversely proportional to the square of the distance”.

Hans Christian Oersted (1777-1851), a Danish physicist, was the first to propose a link between electricity and magnetism. Experiments on the interactions of magnetic and electric fields were carried out by Frenchman Andre Marie Ampere (1775-1836) and Englishman Michael Faraday (1791-1869), but it was the Scotsman James Clerk Maxwell (1831-1879) who laid the theoretical foundation for electromagnetism in the 19th century by demonstrating that electricity and magnetism are the same things.

The work and theoretical models of two Germans, Ernest Ising (1900- ) and Werner Heisenberg (1900- ), are responsible for our current understanding of magnetism, which is based on the theory of electron motion and interactions in atoms (known as quantum electrodynamics) (1901-1976). Werner Heisenberg was a key figure in the development of modern quantum mechanics.

Origin of Magnets

Magnetism is caused by two kinds of electron motions in atoms: one is the motion of electrons in an orbit around the nucleus, which is similar to the motion of planets in our solar system around the sun, and the other is the spin of electrons around their axis, which is similar to the rotation of the Earth around its axis.

Each electron acquires a magnetic moment as a result of its orbital and spin motions, causing it to behave like a tiny magnet. The rotational force experienced by a magnet in a magnetic field of unit strength acting perpendicular to its magnetic axis defines its magnetic moment.

Because of the Pauli exclusion principle, which states that each electronic orbit can only be occupied by two electrons of opposite spin, the magnetic moment of the electrons cancels out in a large fraction of the elements. However, several so-called transition metal atoms, such as iron, cobalt, and nickel, have magnetic moments that are not cancelled, making them common magnetic materials. The magnetic moment in these transition metal elements is derived solely from the spin of the electrons.

The effect of electron orbital motion is not cancelled in the rare earth elements (which start with lanthanum in the sixth row of the Periodic Table of Elements), so both spin and orbital motion contribute to the magnetic moment. Cerium, neodymium, samarium, and europium are examples of magnetic rare earth elements.

Magnetic moments can be found in a wide range of chemical compounds containing transition and rare earth elements, in addition to metals and alloys. Metal oxides, which are chemically bonded compositions of metals with oxygen, are among the most common magnetic compounds.

According to a fundamental law of electromagnetism, a magnetic field is created by the passage of an electric current, the Earth's geomagnetic field is the result of electric currents produced by the slow convective motion of its liquid core.

The Earth's core, according to this model, should be electrically conductive enough to allow for the generation and transmission of an electric current. The resulting geomagnetic field will be dipolar, similar to the magnetic field produced by a conventional magnet, with lines of magnetic force lying in approximate planes passing through the geomagnetic axis.

Who was the Founder of Magnet?

Magnets make the world go-’round, and tales of their discovery and application appear to come from all corners of the globe.

Magnes, a Greek shepherd, is said to have been tending his sheep in Magnesia, a region of northern Greece, around 4,000 years ago. When he took a step forward, the nails holding his shoe together and the metal tip of his staff became stuck to the rock he was standing on! He began digging, intrigued, and found the first known lodestone. Magnesia or Magnesia was probably the inspiration for the name "magnetite" given to lodestones.

Pliny the Elder, a Roman author, and naturalist who undertook important scientific research for the then-Roman Emperor Vespasian in the early AD years described a hill made of a stone that attracted iron. Pliny attributed magnetite's powers to magic, igniting a flurry of superstitious theories about the material, including the possibility that ships that had gone missing at sea had been drawn to magnetic islands. Pliny died in the eruption of Pompeii, which is unrelated but curious.

Scandinavia

With a large lodestone deposit in Scandinavia and insufficient light to navigate ships by during the winter, the Vikings had every incentive to put lodestone's magnetic properties to good use. The Vikings are believed to have used a compass-like tool made of lodestone and iron as early as 1,000 B.C. Viking sailors used a magnetized iron needle inserted into a piece of straw and float in a bowl of water to signify north and south, according to legend.

The Chinese may have invented a mariner's compass that was similar in construction to the Vikings'. As early as 800 A.D., the Chinese used a splinter of lodestone floating on water to navigate. Explorers such as Marco Polo brought the magnetic compass back to Italy, allowing Europeans to finally explore the oceans that the Vikings had been navigating for at least 500 years using their version of the compass.

One of the first written accounts of the scientific properties of magnets was authored by French scholar Petrus Peregrinus in the 1200s. The freely pivoting compass needle–a key component of the first dry compass–is depicted and discussed in his report. Peregrinus is said to have composed these works while taking part in a papal-sanctioned crusade/attack on the Italian city of Lucera.

William Gilbert, a physician from the United Kingdom, was the first scientist to create a magnet. He found in 1600 that magnets could be forged out of iron and that their magnetic properties could be lost when that iron was heated.

Hans Christian Oersted began studying the relationship between electricity and magnetism two hundred years later, in 1820. He proved his theory by placing a magnetic compass near an electrical wire, which caused the compass's accuracy to be thrown off.

A Brief History of Electromagnets/Electromagnetism

1770-90: Cavendish and Coulomb establish foundations of electrostatics

1820: Oersted makes the connection between flowing charge and magnetism.

1820s: Ampere identifies currents as the source of all magnetism (even permanent magnets)

1831: Faraday (also Henry) discovers that time-varying magnetic fields serve as sources for electric fields

1864: Maxwell puts it all together.

1887: Hertz demonstrates the existence of electromagnetic radiation .

History of Electromagnets

Hans Christian Orsted made an unexpected observation while preparing for an evening lecture on April 21, 1820. When the electric current from the battery he was using was turned on and off while he was setting up his materials, he noticed a compass needle deflected away from magnetic north.

This deflection convinced him that magnetic fields, like light and heat, radiate from all sides of a wire carrying an electric current, confirming the existence of a direct relationship between electricity and magnetism.

Orsted did not provide a satisfactory explanation for the phenomenon at the time of its discovery, nor did he attempt to represent it mathematically.

His discoveries sparked a wave of electrodynamics studies across the scientific community. They influenced the development of a single mathematical form to represent the magnetic forces between current-carrying conductors by French physicist André-Marie Ampère. Orsted's discovery was also a significant step toward a unified energy concept.

One of the most important achievements of 19th-century mathematical physics is the unification, which was observed by Michael Faraday, expanded by James Clerk Maxwell, and partially reformulated by Oliver Heaviside and Heinrich Hertz. It had far-reaching implications, one of which was a better understanding of light's nature.

William Sturgeon, an Englishman, was the first person to invent an electromagnet in 1826. It was made up of a coil that created a magnetic field when the current passed through it. There was an iron core in the coil, which increased the magnetic field and led. The magnetic field lines, in this case, are concentrated in the interior of the coil, which has the highest magnetic flux density. With a larger distance outside the coil, it decreases quickly; we can also argue that electromagnets have a large effect when used over short distances.

FAQs on Discovery of Magnets

Q1. State the Different Types of Magnetism.

Ans: On the basis of the magnetic behaviour of materials in response to magnetic fields at various temperatures, five fundamental types of magnetism have been observed and classified.

Ferromagnetism

Ferrimagnetism

Antiferromagnetism

Paramagnetism

Dimagnetism

Q2. Mention the Contemporary Applications of Magnetism.

Ans: Electromagnets are used in motors and generators, as well as in power supplies that convert electrical energy from a wall outlet into direct current energy for a wide range of electronic devices. In MRI (magnetic resonance imaging) devices that are now widely used in hospitals and medical centers, high field superconducting magnets (where superconducting coils produce the magnetic field) provide the magnetic field.

Magnetic recording and storage devices in computers, as well as audio and video systems, are some of the more esoteric applications of magnetism.

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Magnetism:  History of the Magnet

The earliest Chinese reference to “Lodestone” occurs in the 400 BCE in “The Book of the Devil Valley Master.” In this writing, Lushi Chunqiu, from the second century BC stated that Lodestone makes iron come to it or it “attracts” it. By the 12th century, the Chinese were using Lodestone compasses to navigate.

In 1600 English Scientist William Gilbert was the first to investigate magnetism using scientific methods. Gilbert conducted many experiments with his model of the Earth (called the terrella ). From his experiments, he argued that the center of the Earth was iron and that the Earth was, in fact, a magnet and this was the reason that compasses point north, and not due to Polaris (the pole star) or a large magnetic island.

Early theoretical investigations into the Earth’s magnetism were studied by Carl Friedrich Gauss.

The modern understanding of the relationship between magnets and electricity began with Hans Christian Orsted in 1819. Orsted, a Professor at the University of Copenhagen, discovered by accident that an electric current could influence a compass needle.

By the 1930s scientists had produced the first Alnico magnet. By 1966 the first Samarium-Cobalt magnets were produced with an energy capable of 18 MGOe and were refined to be able to achieve 30 MGOe by 1972.

In 1983 joint research between General Motors, Sumitomo Special Metals and the Chinese Academy of Sciences developed  the first 35 MGOe magnet out of Neodymium, Iron and Boron which also comprise the body of today's 52 MGOe magnets.

Today’s rare earth magnets are used in almost every technologically advanced device.

Magnetism:  Magnetic Materials in Use Today

The most common magnetic material in use today are Ceramic, Alnico, Samarium Cobalt, and Neodymium. Each is made up of different elements used for different applications.

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• Published: 04 May 1876

History of Magnetism

• S. J. PERRY  

Nature volume  14 ,  page 10 ( 1876 ) Cite this article

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A PARAGRAPH in the article on “The Early History of Magnetism,” in your last number, contains a passage which requires, I think, a note of explanation. The writer says: “A Latin letter ascribed to Peter Adsiger, 1269, preserved among the manuscripts of the University of Leyden, contains the following remark on the declination of the needle…” Now Humboldt, on the authority of Libri, denies the existence of the passage in the Leyden MSS., affirming that it is only an interpolation in a Paris copy. But what is of more importance, he also states that the title of the letter is “Epistola Ptri P. de Maricourt ad Sigernum de Foucoucourt.” E. Walker, in his well-known essay on Magnetism, refers to Cavallo as quoting the supposed letter of Adsiger.

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Geologists discover rocks with the oldest evidence yet of Earth’s magnetic field

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Geologists at MIT and Oxford University have uncovered ancient rocks in Greenland that bear the oldest remnants of Earth’s early magnetic field.

The rocks appear to be exceptionally pristine, having preserved their properties for billions of years. The researchers determined that the rocks are about 3.7 billion years old and retain signatures of a magnetic field with a strength of at least 15 microtesla. The ancient field is similar in magnitude to the Earth’s magnetic field today.

The open-access findings, appearing today in the Journal of Geophysical Research , represent some of the earliest evidence of a magnetic field surrounding the Earth. The results potentially extend the age of the Earth’s magnetic field by hundreds of millions of years, and may shed light on the planet’s early conditions that helped life take hold.

“The magnetic field is, in theory, one of the reasons we think Earth is really unique as a habitable planet,” says Claire Nichols, a former MIT postdoc who is now an associate professor of the geology of planetary processes at Oxford University. “It’s thought our magnetic field protects us from harmful radiation from space, and also helps us to have oceans and atmospheres that can be stable for long periods of time.”

Previous studies have shown evidence for a magnetic field on Earth that is at least 3.5 billion years old. The new study is extending the magnetic field’s lifetime by another 200 million years.

“That’s important because that’s the time when we think life was emerging,” says Benjamin Weiss, the Robert R. Shrock Professor of Planetary Sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “If the Earth’s magnetic field was around a few hundred million years earlier, it could have played a critical role in making the planet habitable.”

Nichols and Weiss are co-authors of the new study, which also includes Craig Martin and Athena Eyster at MIT, Adam Maloof at Princeton University, and additional colleagues from institutions including Tufts University and the University of Colorado at Boulder.

A slow churn

Today, the Earth’s magnetic field is powered by its molten iron core, which slowly churns up electric currents in a self-generating “dynamo.” The resulting magnetic field extends out and around the planet like a protective bubble. Scientists suspect that, early in its evolution, the Earth was able to foster life, in part due to an early magnetic field that was strong enough to retain a life-sustaining atmosphere and simultaneously shield the planet from damaging solar radiation.

Exactly how early and robust this magnetic shield was is up for debate, though there has been evidence dating its existence to about 3.5 billion years ago.

“We wanted to see if we could extend this record back beyond 3.5 billion years and nail down how strong that early field was,” Nichols says.

In 2018, as a postdoc working in Weiss’ lab at the time, Nichols and her team set off on an expedition to the Isua Supracrustal Belt, a 20-mile stretch of exposed rock formations surrounded by towering ice sheets in the southwest of Greenland. There, scientists have discovered the oldest preserved rocks on Earth, which have been extensively studied in hopes of answering a slew of scientific questions about Earth’s ancient conditions.

For Nichols and Weiss, the objective was to find rocks that still held signatures of the Earth’s magnetic field when the rocks first formed. Rocks form through many millions of years, as grains of sediment and minerals accumulate and are progressively packed and buried under subsequent deposition over time. Any magnetic minerals such as iron-oxides that are in the deposits follow the pull of the Earth’s magnetic field as they form. This collective orientation, and the imprint of the magnetic field, are preserved in the rocks.

However, this preserved magnetic field can be scrambled and completely erased if the rocks subsequently undergo extreme thermal or aqueous events such as hydrothermal activity or plate tectonics that can pressurize and crush up these deposits. Determining the age of a magnetic field in ancient rocks has therefore been a highly contested area of study.

To get to rocks that were hopefully preserved and unaltered since their original deposition, the team sampled from rock formations in the Isua Supracrustal Belt, a remote location that was only accessible by helicopter.

“It’s about 150 kilometers away from the capital city, and you get helicoptered in, right up against the ice sheet,” Nichols says. “Here, you have the world’s oldest rocks essentially, surrounded by this dramatic expression of the ice age. It’s a really spectacular place.”

Dynamic history

The team returned to MIT with whole rock samples of banded iron formations — a rock type that appears as stripes of iron-rich and silica-rich rock. The iron-oxide minerals found in these rocks can act as tiny magnets that orient with any external magnetic field. Given their composition, the researchers suspect the rocks were originally formed in primordial oceans prior to the rise in atmospheric oxygen around 2.5 billion years ago.

“Back when there wasn’t oxygen in the atmosphere, iron didn’t oxidize so easily, so it was in solution in the oceans until it reached a critical concentration, when it precipitated out,” Nichols explains. “So, it’s basically a result of iron raining out of the oceans and depositing on the seafloor.”

“They’re very beautiful, weird rocks that don’t look like anything that forms on Earth today,” Weiss adds.

Previous studies had used uranium-lead dating to determine the age of the iron oxides in these rock samples. The ratio of uranium to lead (U-Pb) gives scientists an estimate of a rock’s age. This analysis found that some of the magnetized minerals were likely about 3.7 billion years old. The MIT team, in collaboration with researchers from Rensselaer Polytechnic Institute, showed in a paper published last year that the U-Pb age also dates the age of the magnetic record in these minerals.

The researchers then set out to determine whether the ancient rocks preserved magnetic field from that far back, and how strong that field might have been.

“The samples we think are best and have that very old signature, we then demagnetize in the lab, in steps. We apply a laboratory field that we know the strength of, and we remagnetize the rocks in steps, so you can compare the gradient of the demagnetization to the gradient of the lab magnetization. That gradient tells you how strong the ancient field was,” Nichols explains.

Through this careful process of remagnetization, the team concluded that the rocks likely harbored an ancient, 3.7-billion-year-old magnetic field, with a magnitude of at least 15 microtesla. Today, Earth’s magnetic field measures around 30 microtesla.

“It’s half the strength, but the same order of magnitude,” Nichols says. “The fact that it’s similar in strength as today’s field implies whatever is driving Earth’s magnetic field has not changed massively in power over billions of years.”

The team’s experiments also showed that the rocks retained the ancient field, despite having undergone two subsequent thermal events. Any extreme thermal event, such as a tectonic shake-up of the subsurface or hydrothermal eruptions, could potentially heat up and erase a rock’s magnetic field. But the team found that the iron in their samples likely oriented, then crystallized, 3.7 billion years ago, in some initial, extreme thermal event. Around 2.8 billion years ago, and then again at 1.5 billion years ago, the rocks may have been reheated, but not to the extreme temperatures that would have scrambled their magnetization.

“The rocks that the team has studied have experienced quite a bit during their long geological journey on our planet,” says Annique van der Boon, a planetary science researcher at the University of Oslo who was not involved in the study. “The authors have done a lot of work on constraining which geological events have affected the rocks at different times.” 

“The team have taken their time to deliver a very thorough study of these complex rocks, which do not give up their secrets easily,” says Andy Biggin, professor of geomagnetism at the University of Liverpool, who did not contribute to the study. “These new results tell us that the Earth’s magnetic field was alive and well 3.7 billion years ago. Knowing it was there and strong contributes a significant boundary constraint on the early Earth’s environment.”

The results also raise questions about how the ancient Earth could have powered such a robust magnetic field. While today’s field is powered by crystallization of the solid iron inner core, it’s thought that the inner core had not yet formed so early in the planet’s evolution.

“It seems like evidence for whatever was generating a magnetic field back then was a different power source from what we have today,” Weiss says. “And we care about Earth because there’s life here, but it’s also a touchstone for understanding other terrestrial planets. It suggests planets throughout the galaxy probably have lots of ways of powering a magnetic field, which is important for the question of habitability elsewhere.”

This research was supported, in part, by the Simons Foundation.

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Ancient rocks hold proof of Earth's magnetic field. Here's why that's puzzling

These rocks offer evidence that Earth had a strong magnetic field 3.7 billion years ago, but scientists aren't sure where that field could've come from.

A 3.7-billion-year-old record of our planet's ancient magnetism has been unearthed, providing evidence that Earth's magnetic field already existed very early in history. This discovery, however, is quite surprising.

Rocks approaching 4 billion years old are hard to find; most have been recycled through Earth 's tectonic activity, slipping into the mantle through subduction zones before being belched back out via volcanoes. Yet, somehow,  a sequence of rocks in the Isua Supracrustal Belt in Greenland has survived the ravages of time thanks to its unique geology, situated on top of a thick continental plate like a life-raft amid an ocean of tectonic upheaval.

Now, researchers from the University of Oxford and the Massachusetts Institute of Technology have dug up some of those Isua rocks, finding that they contain an ironclad record of the early Earth's magnetic field. According to this record, our planet's magnetic field doesn't seem to have changed very much at all in the intervening time — but geologists do not fully understand how Earth could have produced a magnetic field at all back then. 

Related: Earth got hammered by cosmic rays 41,000 years ago due to a weak magnetic field

The existence of a magnetic field is crucial for the development of life on Earth, with field lines warding off the hazardous sleet of charged particles blown towards us via the solar wind . The existence of an early magnetic field could have thus helped life get a foothold on our planet.

Previously, estimates and hints of the early Earth's magnetic field have come from individual mineral crystals called zircons found within ancient rocks from Western Australia. These had suggested the existence of a magnetic field 4.2 billion years ago . However, those results were subsequently doubted as unreliable. 

The new results from the Greenland rocks are considered more reliable because, for the first time, they are based on entire iron-bearing rocks (rather than individual mineral crystals) to derive the primordial field strength. Therefore, the sample offers the first solid measure of not only the strength of Earth's ancient magnetic field, but also of the timing of when the magnetic field originally appeared.

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"Extracting reliable records from rocks this old is extremely challenging, and it was really exciting to see primary magnetic signals begin to emerge when we analyzed these samples in the lab," said lead researcher Claire Nichols, who is a professor of planetary geology at the University of Oxford, in a press statement . "This is a really important step forward as we try and determine the role of the ancient magnetic field when life on Earth was first emerging."

The iron particles within the Isua rocks can be thought of  like tiny magnets, aligning with Earth's magnetic field when the rock around them first crystallized 3.7 billion years ago. Their alignment therefore holds a record of the field's strength. That strength is measured to have been at least 15 microtesla (mT), which is comparable to Earth's field strength of 30 mT today.

This still leaves that earlier puzzle, however: How did the early Earth produce its magnetic field? 

— Debris from burning satellites could be affecting Earth's magnetic field

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Today, that field is produced by the dynamo effect generated by electrical currents in the molten iron outer core of the Earth, an effect stirred up by buoyancy forces as the planet's inner core cools and solidifies. However, the inner core only grew cool enough to begin solidifying about a billion years ago; 3.7 billion years ago, it could not have influenced a dynamo effect in the same way that it does today. In short, how Earth's ancient magnetic field was generated remains a mystery.

Thankfully, it was indeed generated, and it surely helped primitive microbial life survive and evolve. The solar wind was stronger in the past than it is today, but as time went by, the Earth's magnetic field would have been able to stand up to it, creating conditions for life to move out of the oceans, where it was protected from harmful radiation, and onto land.

The findings were published on April 24 in the Journal of Geophysical Research .

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

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• newtons_laws The article says "That strength is measured to have been at least 15 microtesla (mT), which is comparable to Earth's field strength of 30 mT today." mT is incorrect; the internationally recognised prefix 'm' stands for for milli (one thousandth), the correct way of expressing a microtesla is μT (one millionth of a Tesla). Reply
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Every new generation of eyes sees a new version of our galaxy, the Milky Way.

This Impressionistic swirl of color represents the churning magnetic fields in giant dust clouds near the center of the galaxy.

The map, painted in infrared wavelengths, reveals new details in a stretch of our galactic home 500 light-years wide.

The colors represent different temperatures of interstellar dust. Cool, dense dust is green; warmer dust is pink. The magnetic field lines, showing the direction of force, were undetectable before now.

The map is a first step toward understanding how magnetism can shape the universe.

The Magnetic Heart of the Milky Way

By Dennis Overbye

“The nation that controls magnetism will control the universe.” So maintained Dick Tracy, the fictional detective in the comic strip by Chester Gould, in 1962.

But does magnetism control the universe, too?

About seven stars are born each year in the Milky Way, our home galaxy. They come from dust and to dust they eventually return. Now, a celestial image, an Impressionistic swirl of color in the center of the Milky Way, represents a first step toward understanding the role of those magnetic fields in the cycle of stellar death and rebirth.

The image was produced by David Chuss, a physicist at Villanova University and an international team of astronomers. The project is known as FIREPLACE, for Far-InfraRed Polarimetric Large Area CMZ Exploration. The team’s map reveals previously invisible details in a stretch of the central Milky Way 500 light-years wide.

The colors represent different temperatures of interstellar dust: Green indicates cool, dense dust; pink indicates warmer dust. Threaded through these hues are lines showing the directions of magnetic force in the clouds. The yellow streaks are jets of hot ionized gas, which emits radio waves. The jets were first recorded two years ago by the MeerKAT radio telescope in South Africa.

Every new generation of eyes sees a new version of our galaxy.

To map the galaxy’s magnetic field lines, Dr. Chuss and his colleagues flew at 45,000 feet aboard the Stratospheric Observatory for Infrared Astronomy, or SOFIA, a 747 outfitted for astronomy. A special spectrograph measured the direction of polarization of the infrared light emanating from the dust, revealing the directions of the magnetic fields point by point.

The center of the Milky Way is barely noticeable to the right of center in the map, just below a small blob that resembles a sideways figure eight. At the middle of the dusty blob is a monster black hole, around which the entire galaxy rotates like a carousel.

“The next step is to figure out what this all means,” Dr. Chuss said in an interview. Embedded in this map could be clues to some of nature’s deepest, most complex processes, including how stars, the sources of all light and life in the universe, come to be.

“It will provide the ability for new theories to be tested,” Dr. Chuss said, “and guide the development of the next generation of astronomical exploration.”

Produced by Antonio de Luca and Elijah Walker . Image: Villanova University/Paré, Karpovich, Chuss (PI).

An earlier version of this article misidentified the academic affiliation of David Chuss, a physicist. It is Villanova University, not Vanderbilt University.

How we handle corrections

Dennis Overbye is the cosmic affairs correspondent for The Times, covering physics and astronomy. More about Dennis Overbye

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Brief History of Magnetic Levitation

In the early 1900s, Emile Bache let first conceived of a magnetic suspension using repulsive forces generated by alternating currents. Bache let’s ideas for EDS remained dormant until the 1960s when superconducting magnets became available, because his concept used too much power for conventional conductors. In 1922, Hermann Kemper in Germany pioneered attractive-mode (EMS) Maglev and received a patent for magnetic levitation of trains in 1934.

In 1939-43, the Germans first worked on a real train at the ATE in Goettingen. The basic design for practical attractive-mode maglev was presented by Kemper in 1953. The Tran rapid (TR01) was built in 1969.Maglev development in the U. S. began as a result of the the High-Speed Ground Transportation (HSGT) Act of 1965.

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This act authorized Federal funding for HSGT projects, including rail, air cushion vehicles, and Maglev. This government largesse gave the U. S. researchers an early advantage over their foreign counterparts. Americans pioneered the concept of superconducting magnetic levitation (EDS,) and they dominated early experimental research. As early as 1963, James Powell and Gordon Danby of Brookhaven National Laboratory realized that superconductivity could get around the problems of Bache let’s earlier concepts.

In 1966, Powell and Danby presented their Maglev concept of using superconducting magnets in a vehicle and discrete coils on a guide way. Powell and Danby were awarded a patent in 1968, and their work was eventually adopted by the Japanese for use in their system. Powell and Danby were awarded the 2000 Benjamin Franklin Medal in Engineering by the Franklin Institute for their work on EDS Maglev.In 1969, groups from Stanford, Atomics International and Sandia developed a continuous-sheet guide way (CSG) concept.

In this system, the moving magnetic fields of the vehicle magnets induce currents in a continuous sheet of conducting material such as aluminum. Several groups, including MIT (Kolm and Thornton, MIT, 1972,) built 1/25th scale models and tested them at speeds up to 27 m/s (97.2 km/h.) The CSG concept is alive and well in 2001 with the Magplane.

If a small magnet is brought near a superconductor, it will be repelled because induced super currents will produce mirror images of each pole. If a small permanent magnet is placed above a superconductor, it can be levitated by this repulsive force. The black ceramic material is a sample of the yttrium based superconductor.By tapping with a sharp instrument, the suspended magnet can be caused to oscillate or rotate.

This motion is found to be damped, and will come to rest in a few seconds.The Meissner effect in superconductors like this black ceramic yttrium based superconductor acts to exclude magnetic fields from the material. Since the electrical resistance is zero, super currents are generated in the material to exclude the magnetic fields from a magnet brought near it. The currents which cancel the external field produce magnetic poles which mirror the poles of the permanent magnet, repelling them to provide the lift to levitate the magnet.

The levitation process is quite remarkable. Since the levitating currents in the superconductor meet no resistance, they can adjust almost instantly to maintain the levitation. The suspended magnet can be moved, put into oscillation, or even spun rapidly and the levitation currents will adjust to keep it in suspension.

Levitating pyrolytic graphiteThere are some materials that are more diamagnetic than bismuth. These include superconductors (which at this time require cryogenic temperatures to work), and similar materials that exhibit “giant diamagnetism” (also at very low temperatures).But there is one material that is more diamagnetic than bismuth at room temperature, at least in one direction. That material is called pyrolytic graphite.

Pyrolytic graphite is a synthetic material, made by a process called chemical vapor deposition. To make pyrolytic graphite, methane gas at low pressure (about 1 Torr) is heated to 2000 degrees Celsius. Very slowly, (one thousandth of an inch per hour) a layer of graphite grows. The graphite made this way is very highly ordered, and the layers of carbon atoms form like a crystal of hexagonal sheets.

These sheets lie on top of one another like sheets of mica. You can separate the layers with a sharp knife to make thinner sheets. Pyrolytic graphite is more diamagnetic than bismuth, but only in the direction perpendicular to the sheets of carbon. In other directions, it is still diamagnetic, but not as good as bismuth.

With a piece half a millimeter thick, using neodymium-iron-boron super magnets, you can see from the photos that the piece is levitating about a millimeter above the magnets. To make the pyrolytic graphite plate sit still above the magnet, we need a way to force it towards the center. We can do that by using four magnets. The poles of the magnets push on the diamagnetic material more strongly than other parts of the magnet.

With four magnets, the four edges of the square of pyrolytic graphite will be pushed away from the four poles. If the square is slightly smaller than half the width of the four magnets (a little smaller than one magnet), then we can place it in the center, and it will be pushed to the middle and stay. Since diamagnetic materials are repelled by either pole, we can place the magnets with alternating north and south poles, and they will stick nicely to one another. I like to sit the whole array on a piece of sheet steel, so the magnets stay put.

The pyrolytic graphite plate floats above the magnets and springs back when you push it down with a finger. Since pyrolytic graphite is a little more diamagnetic than bismuth, it makes a great substitute for bismuth in the levitating magnet project.Place the blade carefully in the middle of the edge of the graphite. Slowly push the blade in with a slight rocking motion.

The graphite will make a nice clean sound as it starts to split. Sometimes you will get one thin piece and one thicker piece after they are split. You can often split the thicker piece again, giving you three pieces. If you are very skilled, you can get four pieces, but you will break a few gaining that skill.

Lastly, once the slices are very thin, you can cut them in half by rocking the sharp knife over the middle of each one. The pieces will snap and may fly some distance unless you put a finger over them to hold them down. The thick graphite is too heavy to float on the magnets. The nice thin sheets you split it into will float, and the thinnest ones will float highest.

How can you magnetically levitate objects?Magnetism is fascinating, especially when it is used to cause objects to levitate or float or be suspended in the air, defying the gravity which keeps us on the ground.  How can this be done?  There are 10 ways to magnetically levitate objects:

• Repulsion between like poles of permanent magnets or electromagnets.   However, there needs to be a way to constrain the magnets so they don’t flip over and become attracted to each other. For example, floating donut magnets have the dowel rod in the center to keep them from flipping over.
• Repulsion between a magnet and a metallic conductor induced by relative motion.  However, the magnet needs to be restrained from moving in the same direction as the conductor, otherwise it will travel with the conductor.
• Repulsion between a metallic conductor and an AC electromagnet.  It is possible to shape the magnetic field to keep the conductor constrained in its motions; otherwise, a mechanical means is needed to keep the conductor in place.
• Repulsion between a magnetic field and a diamagnetic substance.  This is the case of the floating frog, and the floating magnet between two diamagnetic disks.
• Repulsion between a magnet and a superconductor. No mechanical constraints are needed for this.
• Attraction between unlike poles of permanent magnets or electromagnets.  This will work as long as there is a mechanical method to constrain the magnets so they don’t touch.
• Attraction between the open core of an electromagnetic solenoid and a piece of iron or a magnet.  The iron or magnet will touch the inside surface of the solenoid.
• Attraction between a permanent magnet or electromagnet and a piece of iron.  Again, the iron needs to be constrained.
• Attraction between an electromagnet and a piece of iron or a magnet, with sensors and active control of the current to the electromagnet used to maintain some distance between them.
• Repulsion between and electromagnet and a magnet, with sensors and active control of the current to the electromagnet used to maintain some distance between them.

The stable levitation of magnets is forbidden by Earn Shaw’s theorem, which statesthat no stationary object made of magnets in a fixed configuration can be held instable equilibrium by any combination of static magnetic or gravitational forces,.Earn Shaw’s theorem can be viewed as a consequence of the Maxwell equations, whichdo not allow the magnitude of a magnetic field in a free space to possess a maximum,as required for stable equilibrium.

Diamagnetism (which respond to magnetic fields withmild repulsion) are known to flout the theorem, as their negative susceptibility resultsin the requirement of a minimum rather than a maximum in the field’s magnitude,Nevertheless, levitation of a magnet without using superconductors is widely thoughtto be impossible. We find that the stable levitation of a magnet can be achieved usingthe feeble diamagnetism of materials that are normally perceived as beingnon-magnetic, so that even human fingers can keep a magnet hovering in mid-airwithout touching it.

Earn Shaw TheoremThe proof of Earn Shaw’s theorem is very simple if you understand some basic vector calculus. The static force as a function of position F(x) acting on any body in vacuum due to gravitation, electrostatic and magneto static fields will always be divergence less.

Because of the small distances, quantum effects are significant but Earn Shaw’s theorem assumes that only classical physics is relevant.Feedback: If you can detect the position of an object in space and feed it into a control system which can vary the strength of electromagnets which are acting on the object, it is not difficult to keep it levitated. You just have to program the system to weaken the strength of the magnet whenever the object approaches it and strengthen when it moves away. You could even do it with movable permanent magnets.

These methods violate the assumption of Earn Shaw’s theorem that the magnets are fixed. Electromagnetic suspension is one system used in magnetic levitation trains (maglev) such as the one at Birmingham airport, England. It is also possible to buy gadgets which levitate objects in this way.Diamagnetism: It is possible to levitate superconductors and other diamagnetic materials.

This is also used in maglev trains. It has become common place to see the new high temperature superconducting materials levitated in this way. A superconductor is perfectly diamagnetic which means it expels a magnetic field. Other diamagnetic materials are common place and can also be levitated in a magnetic field if it is strong enough.

Water droplets and even frogs have been levitated in this way at a magnetic laboratory in the Netherlands (Physics World, April 1997).Earn Shaw’s theorem does not apply to diamagnetic as they behave like “anti-magnets”: they align ANTI-parallel to magnetic lines while the magnets meant in the theorem always try to align in parallel. In diamagnetic, electrons adjust their trajectories to compensate the influence of the external magnetic field and these results in an induced magnetic field which is directed in the opposite direction. It means that the induced magnetic moment is ant parallel to the external field.

Superconductors are diamagnetic with the macroscopic change in trajectories (screening current at the surface). The frog is another example but the electron orbits are changed in every molecule of its body.MethodsThere are several methods to obtain magnetic levitation. The primary ones used in maglev trains are servo-stabilized electromagnetic suspension (EMS), electrodynamics suspension (EDS), and Induct rack.

At some critical velocity the induced magnetic field is strong enough to induce levitation over a series of such loops. The Halbach arrays can be placed in a stable configuration and installed in, for example, a train cart.The Induct rack maglev train system avoids the problems inherent in both the EMS and EDS systems, especially failsafe suspension. It uses only permanent magnets — in a Halbach array mounted in the train cart — and empowered conductive loops installed in the track to provide levitation.

The only requirement for levitation is that the train must already be moving at a few kilometers per hour (roughly the same as walking speed) to keep levitating.The electric current induced in the loop conductors in the track drains energy from the motion of the train (called “magnetic drag”), but efficiency is still good, and no active electronics or cryogenics for superconductors are needed.

Thermodynamics Thermodynamics subtype is electromagnetism and its further subtype leading to Magneto dynamics. As can be seen from this example: The interaction of the electromagnetic fields with various media (liquid and solid metals, liquid semiconductors, plasmas, electrolytes, Ferro fluids) occurs by means of various forces, including Lorentz, Kelvin, and diamagnetic forces.

This allows to control, process, manipulate materials, and to affect their microstructure. Examples of the action of various forces include magnetic levitation of electrically conducting and non-conducting fluids, melting, stirring, pumping, stabilization of melts, free surfaces and interfaces, etc. EPM is involved in the production of metals and alloys (e.g. aluminum, steel, titanium and magnesium alloys), ceramics and glasses of highest purity, semiconductors (Si, GaAs, CdTe), and in efficient control of production of nano-scale metallic and ceramic powders, Ferro fluids for medical and engineering applications, laser welding, etc. Solidification occurs in a wide range of industrial applications, including crystal growth and casting.

The understanding of the solidification processes heavily relies on thermodynamics for describing heat transfer and phase transition phenomena as well as on magneto hydrodynamics for accounting for fluid flows and the appearance of convective instabilities and turbulence. The goal is to better understand the parameters that affect solidification, in particular in relation to external electromagnetic fields or mechanical perturbations, the formation of the mushy zone, and its effect on the microstructure of materials.

Fundamental studies on solidification include model experiments and numerical simulation. The goal is to improve the understanding of free surface and interface instabilities with the aim of controlling the behavior of surfaces of electrically conducting fluids. This includes modeling and experimental work on the stabilization of interfaces using external fields. The numerical description of levitation melting, in which a piece of metal is being simultaneously levitated and melted by the magnetic field generated by a high frequency current is also of particular interest.

• Moon, Francis C. (1994). Superconducting Levitation Applications to Bearings and Magnetic Transportation.
• Braun beck, W. Free suspension of bodies in electric and magnetic fields, Zeitschrift für Physik, 112, 11, pp753-763 (1939)Brandt, Science, Jan 1989·

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Astrophysics > High Energy Astrophysical Phenomena

Title: the impact of different magnetic braking prescriptions on the evolution of lmxbs.

Abstract: We revisit the evolution of low-mass close binary systems under different magnetic braking (MB) prescriptions. We study binaries with a neutron star accretor. During mass transfer episodes, these systems emit X-rays and are known as Low Mass X-ray Binaries (LMXBs). When mass transfer stops, they can be observed as binary pulsars. Additionally, some of these systems can experience mass transfer while having orbital periods of less than 1 hr, thus evolving into ultracompact X-ray binaries (UCXBs). The evolution of LMXBs depends on their capability to lose angular momentum and maintain stable mass transfer. Among the angular momentum loss mechanisms, MB is one important, and still uncertain phenomenon. The standard MB prescription faces some problems when calculating LMXB evolution, leading to, e.g., a fine-tuning problem in the formation of UCXBs. Recent studies proposed new MB prescriptions, yielding diverse outcomes. Here, we investigate the effects of three novel MB prescriptions on the evolution of LMXBs using our stellar code. We found that all MB prescriptions considered allow the formation of binaries with orbital periods spanning from less than one hour to more than tens of days. Remarkably, our results enable the occurrence of wide systems even for the MB law that causes the strongest angular momentum losses and very high mass transfer rates. We found that models computed with the strongest MB prescription reach the UCXB state starting from a wider initial orbital period interval. Finally, we discuss and compare our results with observations and previous studies performed on this topic.

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