Hans Christian Ørsted and the Romantic Legacy in Science Boston Studies in the Philosophy of Science
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Magnetic Fields Magnetism Magnetic Field
PHY2061 Enriched Physics 2 Lecture Notes Magnetic Fields Magnetic Fields Disclaimer: These lecture notes are not meant to replace the course textbook. The content may be incomplete. Some topics may be unclear. These notes are only meant to be a study aid and a supplement to your own notes. Please report any inaccuracies to the professor. Magnetism Is ubiquitous in every-day life! • Refrigerator magnets (who could live without them?) • Coils that deflect the electron beam in a CRT television or monitor • Cassette tape storage (audio or digital) • Computer disk drive storage • Electromagnet for Magnetic Resonant Imaging (MRI) Magnetic Field Magnets contain two poles: “north” and “south”. The force between like-poles repels (north-north, south-south), while opposite poles attract (north-south). This is reminiscent of the electric force between two charged objects (which can have positive or negative charge). Recall that the electric field was invoked to explain the “action at a distance” effect of the electric force, and was defined by: F E = qel where qel is electric charge of a positive test charge and F is the force acting on it. We might be tempted to define the same for the magnetic field, and write: F B = qmag where qmag is the “magnetic charge” of a positive test charge and F is the force acting on it. However, such a single magnetic charge, a “magnetic monopole,” has never been observed experimentally! You cannot break a bar magnet in half to get just a north pole or a south pole. As far as we know, no such single magnetic charges exist in the universe, D. -
(Modern Philosophy) Part I: Fichte to Hegel 9. Walter Benjamin, Der
Notes 1 Idealism and the Justification of the Image 1. J.G. Fichte, The Vocation of Man (New York: Bobbs Merrill, 1956), p.80 (adapted). 2. Idem, The Science of Knowledge (New York: Appleton, Century Crofts, 1970), p.188. 3. Fichte (1956), pp.81f. 4. Ibid., pp.98f. 5. Ibid., pp.124f. 6. Ibid., p.147. 7. For example, the so-called 'Atheismusstreit'. See: F. Copleston, A History of Philosophy, Vol. V, II (Modern Philosophy) Part I: Fichte to Hegel (New York: Doubleday, 1965), pp.lOOff. 8. Friedrich Schlegel, Kritische Schriften (Miinchen: Carl Hanser, 1956), p.46. 9. Walter Benjamin, Der Begriff der Kunstkritik in der Deutschen Romantik in Gesammelten Schriften 1:1 (Frankfurt am Main, 1972), p.26. 10. Quoted in Benjamin (1972), p.37. 11. F. Schlegel, Lucinde (Stuttgart: Reclam, 1963), p.35. 12. F.J.W. Schelling, System of Transcendental Idealism (Charlottesville: Uni versity of Viriginia Press, 1978), p.219. 13. Ibid., p.232. 14. Henrik Steffens, Inledning til Philosophiske Forelasninger i K9benhavn (1803) (New edn) K0benhavn: Gyldendal, 1905), p.21. 15. Ibid., pp.21f. 16. Ibid., p.22. 17. One of the best summaries of Grundtvig's thought in English remains E.L. Allen, Bishop Grundtvig: A Prophet of the North (London: James Clarke, 1949). James Clarke have also published (more recently) an anthology of Grundtvig's writings. A sign of increasing Anglo-Saxon awareness of Grundtvig's significance is the recently formed Anglo Danish conference Grundtvig and England. 18. Henning Fenger, Kierkegaard: The Myths and Their Origins (Newhaven: Yale University Press, 1980), p.84. 19. -
Speculative Geology
15 Speculative Geology DALE E. SNOW We are not at peace with nature now. Whether it is the record-setting rain on the east coast or the raging wildfires in the west, distant news of melting permafrost or bleaching coral reefs, or the unexpected eruption of Mount Kilauea a few miles from here, things seem increasingly, and increasingly violently, out of control. I would like to suggest that there are resources in Schelling’s Naturphilosophie we can use in the twenty-first century to help us think differently about both the power of nature and our own relationship to it. Although Schelling saw himself, and was seen by many, as antagonistic toward the mechanical science of his own time, it would be a mistake—and a missed opportunity—to see his view as a mere Romantic reaction. It is a speculative rethinking of the idea of nature itself that finds a place for even those phenomena which seem most distant and alien. Schelling described his philosophy of nature as “speculative physics” both to distinguish it from what he calls the dogmatic or mechanistic model of nature, and to announce a new approach to natural science, concerned with the original causes of motion in nature (SW III: 275). Since every “natural phenomenon … stands in connection with the last conditions of nature” (SW III: 279), speculative physics can bring us to an understanding of nature as a system. Geology presents an illuminating case of this approach, as can be seen from Schelling’s characteristically enthusiastic introduction to a paper published by Henrik Steffens in Schelling’sJournal of Speculative Physics (Zeitschrift für speculative Physik) on the oxidization and deoxidization of the earth.1 After praising Steffens’ work on a new and better founded science of geology, Schelling reflects darkly on the too long dominant mechanical approach to geology. -
Chapter 7 Magnetism and Electromagnetism
Chapter 7 Magnetism and Electromagnetism Objectives • Explain the principles of the magnetic field • Explain the principles of electromagnetism • Describe the principle of operation for several types of electromagnetic devices • Explain magnetic hysteresis • Discuss the principle of electromagnetic induction • Describe some applications of electromagnetic induction 1 The Magnetic Field • A permanent magnet has a magnetic field surrounding it • A magnetic field is envisioned to consist of lines of force that radiate from the north pole to the south pole and back to the north pole through the magnetic material Attraction and Repulsion • Unlike magnetic poles have an attractive force between them • Two like poles repel each other 2 Altering a Magnetic Field • When nonmagnetic materials such as paper, glass, wood or plastic are placed in a magnetic field, the lines of force are unaltered • When a magnetic material such as iron is placed in a magnetic field, the lines of force tend to be altered to pass through the magnetic material Magnetic Flux • The force lines going from the north pole to the south pole of a magnet are called magnetic flux (φ); units: weber (Wb) •The magnetic flux density (B) is the amount of flux per unit area perpendicular to the magnetic field; units: tesla (T) 3 Magnetizing Materials • Ferromagnetic materials such as iron, nickel and cobalt have randomly oriented magnetic domains, which become aligned when placed in a magnetic field, thus they effectively become magnets Electromagnetism • Electromagnetism is the production -
A History of German-Scandinavian Relations
A History of German – Scandinavian Relations A History of German-Scandinavian Relations By Raimund Wolfert A History of German – Scandinavian Relations Raimund Wolfert 2 A History of German – Scandinavian Relations Table of contents 1. The Rise and Fall of the Hanseatic League.............................................................5 2. The Thirty Years’ War............................................................................................11 3. Prussia en route to becoming a Great Power........................................................15 4. After the Napoleonic Wars.....................................................................................18 5. The German Empire..............................................................................................23 6. The Interwar Period...............................................................................................29 7. The Aftermath of War............................................................................................33 First version 12/2006 2 A History of German – Scandinavian Relations This essay contemplates the history of German-Scandinavian relations from the Hanseatic period through to the present day, focussing upon the Berlin- Brandenburg region and the northeastern part of Germany that lies to the south of the Baltic Sea. A geographic area whose topography has been shaped by the great Scandinavian glacier of the Vistula ice age from 20000 BC to 13 000 BC will thus be reflected upon. According to the linguistic usage of the term -
Chapter 22 Magnetism
Chapter 22 Magnetism 22.1 The Magnetic Field 22.2 The Magnetic Force on Moving Charges 22.3 The Motion of Charged particles in a Magnetic Field 22.4 The Magnetic Force Exerted on a Current- Carrying Wire 22.5 Loops of Current and Magnetic Torque 22.6 Electric Current, Magnetic Fields, and Ampere’s Law Magnetism – Is this a new force? Bar magnets (compass needle) align themselves in a north-south direction. Poles: Unlike poles attract, like poles repel Magnet has NO effect on an electroscope and is not influenced by gravity Magnets attract only some objects (iron, nickel etc) No magnets ever repel non magnets Magnets have no effect on things like copper or brass Cut a bar magnet-you get two smaller magnets (no magnetic monopoles) Earth is like a huge bar magnet Figure 22–1 The force between two bar magnets (a) Opposite poles attract each other. (b) The force between like poles is repulsive. Figure 22–2 Magnets always have two poles When a bar magnet is broken in half two new poles appear. Each half has both a north pole and a south pole, just like any other bar magnet. Figure 22–4 Magnetic field lines for a bar magnet The field lines are closely spaced near the poles, where the magnetic field B is most intense. In addition, the lines form closed loops that leave at the north pole of the magnet and enter at the south pole. Magnetic Field Lines If a compass is placed in a magnetic field the needle lines up with the field. -
08. Ampère and Faraday Darrigol (2000), Chap 1
08. Ampère and Faraday Darrigol (2000), Chap 1. A. Pre-1820. (1) Electrostatics (frictional electricity) • 1780s. Coulomb's description: ! Two electric fluids: positive and negative. ! Inverse square law: It follows therefore from these three tests, that the repulsive force that the two balls -- [which were] electrified with the same kind of electricity -- exert on each other, Charles-Augustin de Coulomb follows the inverse proportion of (1736-1806) the square of the distance."" (2) Magnetism: Coulomb's description: • Two fluids ("astral" and "boreal") obeying inverse square law. • No magnetic monopoles: fluids are imprisoned in molecules of magnetic bodies. (3) Galvanism • 1770s. Galvani's frog legs. "Animal electricity": phenomenon belongs to biology. • 1800. Volta's ("volatic") pile. Luigi Galvani (1737-1798) • Pile consists of alternating copper and • Charged rod connected zinc plates separated by to inner foil. brine-soaked cloth. • Outer foil grounded. • A "battery" of Leyden • Inner and outer jars that can surfaces store equal spontaeously recharge but opposite charges. themselves. 1745 Leyden jar. • Volta: Pile is an electric phenomenon and belongs to physics. • But: Nicholson and Carlisle use voltaic current to decompose Alessandro Volta water into hydrogen and oxygen. Pile belongs to chemistry! (1745-1827) • Are electricity and magnetism different phenomena? ! Electricity involves violent actions and effects: sparks, thunder, etc. ! Magnetism is more quiet... Hans Christian • 1820. Oersted's Experimenta circa effectum conflictus elecrici in Oersted (1777-1851) acum magneticam ("Experiments on the effect of an electric conflict on the magnetic needle"). ! Galvanic current = an "electric conflict" between decompositions and recompositions of positive and negative electricities. ! Experiments with a galvanic source, connecting wire, and rotating magnetic needle: Needle moves in presence of pile! "Otherwise one could not understand how Oersted's Claims the same portion of the wire drives the • Electric conflict acts on magnetic poles. -
Revision Pack Topic 7- Magnetism & Electromagnetism
Revision Pack Topic 7- Magnetism & Electromagnetism Permanent and induced magnetism, magnetic forces and fields R/A/G Poles of a magnet The poles of a magnet are the places where the magnetic forces are strongest. When two magnets are brought close together they exert a force on each other. Two like poles repel each other. Two unlike poles attract each other. Attraction and repulsion between two magnetic poles are examples of non-contact force. A permanent magnet produces its own magnetic field. An induced magnet is a material that becomes a magnet when it is placed in a magnetic field. Induced magnetism always causes a force of attraction. When removed from the magnetic field an induced magnet loses most/all of its magnetism quickly. Magnetic fields The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel) is called the magnetic field. The force between a magnet and a magnetic material is always one of attraction. The strength of the magnetic field depends on the distance from the magnet. The field is strongest at the poles of the magnet. The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet. A magnetic compass contains a small bar magnet. The Earth has a magnetic field. The compass needle points in the direction of the Earth’s magnetic field. -
Electricity and Magnetism Inductance Transformers Maxwell's Laws
Electricity and Magnetism Inductance Transformers Maxwell's Laws Lana Sheridan De Anza College Dec 1, 2015 Last time • Ampere's law • Faraday's law • Lenz's law Overview • induction and energy transfer • induced electric fields • inductance • self-induction • RL Circuits Inductors A capacitor is a device that stores an electric field as a component of a circuit. inductor a device that stores a magnetic field in a circuit It is typically a coil of wire. 782 Chapter 26 Capacitance and Dielectrics ▸ 26.2 continued Categorize Because of the spherical symmetry of the sys- ϪQ tem, we can use results from previous studies of spherical Figure 26.5 (Example 26.2) systems to find the capacitance. A spherical capacitor consists of an inner sphere of radius a sur- ϩQ a Analyze As shown in Chapter 24, the direction of the rounded by a concentric spherical electric field outside a spherically symmetric charge shell of radius b. The electric field b distribution is radial and its magnitude is given by the between the spheres is directed expression E 5 k Q /r 2. In this case, this result applies to radially outward when the inner e sphere is positively charged. 820 the field Cbetweenhapter 27 the C spheresurrent and (a R esistance, r , b). b S Write an expression for the potential difference between 2 52 ? S 782 Chapter 26 Capacitance and DielectricsTable 27.3 CriticalVb TemperaturesVa 3 E d s a the two conductors from Equation 25.3: for Various Superconductors ▸ 26.2 continued Material Tc (K) b b dr 1 b ApplyCategorize the result Because of Example of the spherical 24.3 forsymmetry the electric ofHgBa the sys 2fieldCa- 2Cu 3O8 2 52134 52 Ϫ5Q Vb Va 3 Er dr ke Q 3 2 ke Q Tl—Ba—Ca—Cu—O 125a a r r a outsidetem, wea sphericallycan use results symmetric from previous charge studies distribution of spherical Figure 26.5 (Example 26.2) systems to findS the capacitance. -
The Idea of the University by Henrik Steffens (1809)
Henrik Steffens held these talks in 1808/1809 in the time of Napoleon’s occupation. The Emperor had just lifted his ban on university teaching. This was, amazingly enough, the formative time of Berlin University, an enterprise that would involve Steffens, Wilhelm von Humboldt, Friedrich Wilhelm Joseph Schelling, Johann Gottlieb Fichte, Friedrich Schleiermacher, Savigny and others. The lectures here were addressed to the students, not the administration or the prevailing governmental authorities. That in itself was quite a statement in these times. To Steffens, a university wasn’t supposed to be merely a trade school, but a place that opened you up, allowed you to blossom as an individual and helped you to learn to embrace the things of this world. We bring here in English, his first talk on the theme of what a university might be. --TCR The Idea of the University by Henrik Steffens (1809) Introduction These lectures were held at the commencement of the winter semester 1808/1809. Illness and various duties have, until now, prevented me from putting them into their current form. As my lectures are always extemporaneous, the reader will not find an exact reproduction of them but rather the succession of the ideas they contained. An esteemed person from abroad has spoken about the qualities of German Universities, as they must appear to a foreigner. One of the foremost minds of this nation has elaborated on the theme, deepening our understanding of it as it applies to this country1. It seems to me by no means superfluous to give the students themselves information about academic learning. -
Faraday and the Electromagnetic Theory of Light - Openmind Search Private Area
8/9/2015 Faraday and the Electromagnetic Theory of Light - OpenMind Search Private area Sharing knowledge for a better future Home Faraday and the Electromagnetic Theory of Light Faraday and the Electromagnetic Theory of Light Share 24 August 2015 Physics, Science Sign in or register to rate this publication Michael Faraday (1791-1867) is probably best known for his discovery of electromagnetic induction, his contributions to electrical engineering and electrochemistry or due to the fact that he was responsible for introducing the concept of field in physics to describe electromagnetic interaction. But perhaps it is not so well known that he also made fundamental contributions to the electromagnetic theory of light. In 1845, just 170 years ago, Faraday discovered that a magnetic field influenced polarized light – a phenomenon known as the magneto-optical effect or Faraday effect. To be precise, he found that the plane of vibration of a beam of linearly polarized light incident on a piece of glass rotated when a magnetic field was applied in the direction of propagation of the beam. This was one of the first indications that electromagnetism and light were related. The following year, in May 1846, Faraday published the article Thoughts on Ray Vibrations, a prophetic publication in which he speculated that light could be a vibration of the electric and magnetic lines of force. Michael Faraday (1791-1867) / Credits: Wikipedia Faraday’s case is not common in the history of physics: although his training was very basic, the laws of electricity and magnetism are due much more to Faraday’s experimental discoveries than to any other https://www.bbvaopenmind.com/en/faraday-electromagnetic-theory-light/ 1/7 8/9/2015 Faraday and the Electromagnetic Theory of Light - OpenMind scientist. -
Magnetism in Transition Metal Complexes
Magnetism for Chemists I. Introduction to Magnetism II. Survey of Magnetic Behavior III. Van Vleck’s Equation III. Applications A. Complexed ions and SOC B. Inter-Atomic Magnetic “Exchange” Interactions © 2012, K.S. Suslick Magnetism Intro 1. Magnetic properties depend on # of unpaired e- and how they interact with one another. 2. Magnetic susceptibility measures ease of alignment of electron spins in an external magnetic field . 3. Magnetic response of e- to an external magnetic field ~ 1000 times that of even the most magnetic nuclei. 4. Best definition of a magnet: a solid in which more electrons point in one direction than in any other direction © 2012, K.S. Suslick 1 Uses of Magnetic Susceptibility 1. Determine # of unpaired e- 2. Magnitude of Spin-Orbit Coupling. 3. Thermal populations of low lying excited states (e.g., spin-crossover complexes). 4. Intra- and Inter- Molecular magnetic exchange interactions. © 2012, K.S. Suslick Response to a Magnetic Field • For a given Hexternal, the magnetic field in the material is B B = Magnetic Induction (tesla) inside the material current I • Magnetic susceptibility, (dimensionless) B > 0 measures the vacuum = 0 material response < 0 relative to a vacuum. H © 2012, K.S. Suslick 2 Magnetic field definitions B – magnetic induction Two quantities H – magnetic intensity describing a magnetic field (Système Internationale, SI) In vacuum: B = µ0H -7 -2 µ0 = 4π · 10 N A - the permeability of free space (the permeability constant) B = H (cgs: centimeter, gram, second) © 2012, K.S. Suslick Magnetism: Definitions The magnetic field inside a substance differs from the free- space value of the applied field: → → → H = H0 + ∆H inside sample applied field shielding/deshielding due to induced internal field Usually, this equation is rewritten as (physicists use B for H): → → → B = H0 + 4 π M magnetic induction magnetization (mag.