Electromagnetic Induction
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Gustav Robert Kirchhoff War Der Sohn Eines Landrichters
Akademischer Werdegang *12.03.1824 in Königsberg (heute: Kaliningrad) Besuch des Kneiphöschen Gymnasiums in Königsberg ab 1842 Studium der Mathematik und Physik an der Universität Königsberg 1847 Promotion in Berlin 1850 Berufung zum außerordentlichen Professor nach Breslau (Polen) 1854 Professor für Physik an der Universität Heidelberg 1874 – 1886 Professor für mathematische Physik in Berlin 1876 Cothenius – Medaille der Leopoldina als Auszeichnung für [1] wissenschaftliches Arbeiten † 17.10.1887 in Berlin Gustav Robert Kirchhoff war der Sohn eines Landrichters. Während des Studiums in seiner Heimatstadt wurde er u. a. von den Professoren F.E. Neumann und F. J. Richelot gelehrt. Im Physikseminar von Neumann verfasste Kirchhoff mit 21 Jahren seine erste Arbeit über den Durchgang der Elektrizität durch Platten. Während der Promotions- und Habilitationsphase an der Universität Berlin entwickelte sich eine Freundschaft mit dem Universalgenie H. Helmholtz. Kirchhoff folgte schließlich der Berufung zum außerordentlichen Professor nach Breslau, wo er R. W. Bunsen, den Erfinder des Bunsenbrenners kennen lernte. Dieser wechselte zur Universität nach Heidelberg, worauf ihm Kirchhoff folgte. Gemeinsam veröffentlichten sie zahlreiche Schriften und entdeckten, wie verschiedene chemische Elemente die Flamme eines Gasbrenners färben. Sie prägten die Spektralanalyse als physikalische Analysemethode und konnten mit ihrer Hilfe eine Erklärung der Frauenhoferlinie finden. Außerdem verzeichneten sie die Entdeckung der Elemente Caesium und Rubidium. Des Weiteren entstand bei Experimenten der Spektralanalyse der Kirchhoffsche Strahlungssatz. Kirchhoffs und Bunsens erster Spektralapparat [2] Kirchhoff arbeitete auch an der Plattentheorie. Der Piola-Kirchhoff-Spannungstensor, die Kirchhoff-Love- Hypothese und die sogenannten Kirchhoff-Platten erinnern daran. 1857 heiratete er Clara Richelot, die Tochter seines Professors für Mathematik. Gemeinsam bekamen sie vier Kinder und führten eine glückliche Ehe. -
3.Joule's Experiments
The Force of Gravity Creates Energy: The “Work” of James Prescott Joule http://www.bookrags.com/biography/james-prescott-joule-wsd/ James Prescott Joule (1818-1889) was the son of a successful British brewer. He tinkered with the tools of his father’s trade (particularly thermometers), and despite never earning an undergraduate degree, he was able to answer two rather simple questions: 1. Why is the temperature of the water at the bottom of a waterfall higher than the temperature at the top? 2. Why does an electrical current flowing through a conductor raise the temperature of water? In order to adequately investigate these questions on our own, we need to first define “temperature” and “energy.” Second, we should determine how the measurement of temperature can relate to “heat” (as energy). Third, we need to find relationships that might exist between temperature and “mechanical” energy and also between temperature and “electrical” energy. Definitions: Before continuing, please write down what you know about temperature and energy below. If you require more space, use the back. Temperature: Energy: We have used the concept of gravity to show how acceleration of freely falling objects is related mathematically to distance, time, and speed. We have also used the relationship between net force applied through a distance to define “work” in the Harvard Step Test. Now, through the work of Joule, we can equate the concepts of “work” and “energy”: Energy is the capacity of a physical system to do work. Potential energy is “stored” energy, kinetic energy is “moving” energy. One type of potential energy is that induced by the gravitational force between two objects held at a distance (there are other types of potential energy, including electrical, magnetic, chemical, nuclear, etc). -
Quantum Mechanics Electromotive Force
Quantum Mechanics_Electromotive force . Electromotive force, also called emf[1] (denoted and measured in volts), is the voltage developed by any source of electrical energy such as a batteryor dynamo.[2] The word "force" in this case is not used to mean mechanical force, measured in newtons, but a potential, or energy per unit of charge, measured involts. In electromagnetic induction, emf can be defined around a closed loop as the electromagnetic workthat would be transferred to a unit of charge if it travels once around that loop.[3] (While the charge travels around the loop, it can simultaneously lose the energy via resistance into thermal energy.) For a time-varying magnetic flux impinging a loop, theElectric potential scalar field is not defined due to circulating electric vector field, but nevertheless an emf does work that can be measured as a virtual electric potential around that loop.[4] In a two-terminal device (such as an electrochemical cell or electromagnetic generator), the emf can be measured as the open-circuit potential difference across the two terminals. The potential difference thus created drives current flow if an external circuit is attached to the source of emf. When current flows, however, the potential difference across the terminals is no longer equal to the emf, but will be smaller because of the voltage drop within the device due to its internal resistance. Devices that can provide emf includeelectrochemical cells, thermoelectric devices, solar cells and photodiodes, electrical generators,transformers, and even Van de Graaff generators.[4][5] In nature, emf is generated whenever magnetic field fluctuations occur through a surface. -
Electro Magnetic Fields Lecture Notes B.Tech
ELECTRO MAGNETIC FIELDS LECTURE NOTES B.TECH (II YEAR – I SEM) (2019-20) Prepared by: M.KUMARA SWAMY., Asst.Prof Department of Electrical & Electronics Engineering MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) Recognized under 2(f) and 12 (B) of UGC ACT 1956 (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Kompally), Secunderabad – 500100, Telangana State, India ELECTRO MAGNETIC FIELDS Objectives: • To introduce the concepts of electric field, magnetic field. • Applications of electric and magnetic fields in the development of the theory for power transmission lines and electrical machines. UNIT – I Electrostatics: Electrostatic Fields – Coulomb’s Law – Electric Field Intensity (EFI) – EFI due to a line and a surface charge – Work done in moving a point charge in an electrostatic field – Electric Potential – Properties of potential function – Potential gradient – Gauss’s law – Application of Gauss’s Law – Maxwell’s first law, div ( D )=ρv – Laplace’s and Poison’s equations . Electric dipole – Dipole moment – potential and EFI due to an electric dipole. UNIT – II Dielectrics & Capacitance: Behavior of conductors in an electric field – Conductors and Insulators – Electric field inside a dielectric material – polarization – Dielectric – Conductor and Dielectric – Dielectric boundary conditions – Capacitance – Capacitance of parallel plates – spherical co‐axial capacitors. Current density – conduction and Convection current densities – Ohm’s law in point form – Equation of continuity UNIT – III Magneto Statics: Static magnetic fields – Biot‐Savart’s law – Magnetic field intensity (MFI) – MFI due to a straight current carrying filament – MFI due to circular, square and solenoid current Carrying wire – Relation between magnetic flux and magnetic flux density – Maxwell’s second Equation, div(B)=0, Ampere’s Law & Applications: Ampere’s circuital law and its applications viz. -
On the First Electromagnetic Measurement of the Velocity of Light by Wilhelm Weber and Rudolf Kohlrausch
Andre Koch Torres Assis On the First Electromagnetic Measurement of the Velocity of Light by Wilhelm Weber and Rudolf Kohlrausch Abstract The electrostatic, electrodynamic and electromagnetic systems of units utilized during last century by Ampère, Gauss, Weber, Maxwell and all the others are analyzed. It is shown how the constant c was introduced in physics by Weber's force of 1846. It is shown that it has the unit of velocity and is the ratio of the electromagnetic and electrostatic units of charge. Weber and Kohlrausch's experiment of 1855 to determine c is quoted, emphasizing that they were the first to measure this quantity and obtained the same value as that of light velocity in vacuum. It is shown how Kirchhoff in 1857 and Weber (1857-64) independently of one another obtained the fact that an electromagnetic signal propagates at light velocity along a thin wire of negligible resistivity. They obtained the telegraphy equation utilizing Weber’s action at a distance force. This was accomplished before the development of Maxwell’s electromagnetic theory of light and before Heaviside’s work. 1. Introduction In this work the introduction of the constant c in electromagnetism by Wilhelm Weber in 1846 is analyzed. It is the ratio of electromagnetic and electrostatic units of charge, one of the most fundamental constants of nature. The meaning of this constant is discussed, the first measurement performed by Weber and Kohlrausch in 1855, and the derivation of the telegraphy equation by Kirchhoff and Weber in 1857. Initially the basic systems of units utilized during last century for describing electromagnetic quantities is presented, along with a short review of Weber’s electrodynamics. -
Electromotive Force
Voltage - Electromotive Force Electrical current flow is the movement of electrons through conductors. But why would the electrons want to move? Electrons move because they get pushed by some external force. There are several energy sources that can force electrons to move. Chemical: Battery Magnetic: Generator Light (Photons): Solar Cell Mechanical: Phonograph pickup, crystal microphone, antiknock sensor Heat: Thermocouple Voltage is the amount of push or pressure that is being applied to the electrons. It is analogous to water pressure. With higher water pressure, more water is forced through a pipe in a given time. With higher voltage, more electrons are pushed through a wire in a given time. If a hose is connected between two faucets with the same pressure, no water flows. For water to flow through the hose, it is necessary to have a difference in water pressure (measured in psi) between the two ends. In the same way, For electrical current to flow in a wire, it is necessary to have a difference in electrical potential (measured in volts) between the two ends of the wire. A battery is an energy source that provides an electrical difference of potential that is capable of forcing electrons through an electrical circuit. We can measure the potential between its two terminals with a voltmeter. Water Tank High Pressure _ e r u e s g s a e t r l Pump p o + v = = t h g i e h No Pressure Figure 1: A Voltage Source Water Analogy. In any case, electrostatic force actually moves the electrons. -
Alessandro Volta
Alessandro Volta Alessandro Volta was born in Como, Lombardy, Italy, on February 18, 1745 and died in 1827. He was known for his most famous invention the battery. He was a physicist, chemist and a pioneer of electrical science. He came from a noble family. Until the age of four, Alessandro showed no signs of talking, and his family feared he was not very intelligent. Fortunately, they were wrong as he grew to be very intelligent. Although as a child he was slow to start speaking, he left school being fluent in Latin, French, English, and German. His language talents helped him in later life when he travelled and discussed science with others around the world. In 1775 he devised the electrophorus - a device that produced a static electric charge. He studied gas chemistry and discovered methane. He created experiments such as the ignition of gases by an electric spark. In 1800 he developed the votaic pile, which was the forerunner of the electric battery which produced a steady electric current. He didn’t intend to invent the battery, but to instead perform science experiments to prove another Italian scientist, Luigi Galvani, was incorrect in his scientific ideas. Alessandro set out to prove Galvani’s idea that animal electricity was the same as static electricity was an incorrect theory. In 1792 Volta performed experiments on dead and disembodied frogs legs. He found out that the key to getting them to move is by contacting two different types of metals; if you use the same type of metal the electricity did not pass through the frog. -
The Concept of Field in the History of Electromagnetism
The concept of field in the history of electromagnetism Giovanni Miano Department of Electrical Engineering University of Naples Federico II ET2011-XXVII Riunione Annuale dei Ricercatori di Elettrotecnica Bologna 16-17 giugno 2011 Celebration of the 150th Birthday of Maxwell’s Equations 150 years ago (on March 1861) a young Maxwell (30 years old) published the first part of the paper On physical lines of force in which he wrote down the equations that, by bringing together the physics of electricity and magnetism, laid the foundations for electromagnetism and modern physics. Statue of Maxwell with its dog Toby. Plaque on E-side of the statue. Edinburgh, George Street. Talk Outline ! A brief survey of the birth of the electromagnetism: a long and intriguing story ! A rapid comparison of Weber’s electrodynamics and Maxwell’s theory: “direct action at distance” and “field theory” General References E. T. Wittaker, Theories of Aether and Electricity, Longam, Green and Co., London, 1910. O. Darrigol, Electrodynamics from Ampère to Einste in, Oxford University Press, 2000. O. M. Bucci, The Genesis of Maxwell’s Equations, in “History of Wireless”, T. K. Sarkar et al. Eds., Wiley-Interscience, 2006. Magnetism and Electricity In 1600 Gilbert published the “De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure” (On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth). ! The Earth is magnetic ()*+(,-.*, Magnesia ad Sipylum) and this is why a compass points north. ! In a quite large class of bodies (glass, sulphur, …) the friction induces the same effect observed in the amber (!"#$%&'(, Elektron). Gilbert gave to it the name “electricus”. -
Magnetism Known to the Early Chinese in 12Th Century, and In
Magnetism Known to the early Chinese in 12th century, and in some detail by ancient Greeks who observed that certain stones “lodestones” attracted pieces of iron. Lodestones were found in the coastal area of “Magnesia” in Thessaly at the beginning of the modern era. The name of magnetism derives from magnesia. William Gilbert, physician to Elizabeth 1, made magnets by rubbing Fe against lodestones and was first to recognize the Earth was a large magnet and that lodestones always pointed north-south. Hence the use of magnetic compasses. Book “De Magnete” 1600. The English word "electricity" was first used in 1646 by Sir Thomas Browne, derived from Gilbert's 1600 New Latin electricus, meaning "like amber". Gilbert demonstrates a “lodestone” compass to ER 1. Painting by Auckland Hunt. John Mitchell (1750) found that like electric forces magnetic forces decrease with separation (conformed by Coulomb). Link between electricity and magnetism discovered by Hans Christian Oersted (1820) who noted a wire carrying an electric current affected a magnetic compass. Conformed by Andre Marie Ampere who shoes electric currents were source of magnetic phenomena. Force fields emanating from a bar magnet, showing Nth and Sth poles (credit: Justscience 2017) Showing magnetic force fields with Fe filings (Wikipedia.org.) Earth’s magnetic field (protects from damaging charged particles emanating from sun. (Credit: livescience.com) Magnetic field around wire carrying a current (stackexchnage.com) Right hand rule gives the right sign of the force (stackexchnage.com) Magnetic field generated by a solenoid (miniphyiscs.com) Van Allen radiation belts. Energetic charged particles travel along B lines Electric currents (moving charges) generate magnetic fields but can magnetic fields generate electric currents. -
Faraday's Law Da
Faraday's Law dA B B r r Φ≡B •d A B ∫ dΦ ε= − B dt Faraday’s Law of Induction r r Recall the definition of magnetic flux is ΦB =B∫ ⋅ d A Faraday’s Law is the induced EMF in a closed loop equal the negative of the time derivative of magnetic flux change in the loop, d r r dΦ ε= −B∫ d ⋅= A − B dt dt Constant B field, changing B field, no induced EMF causes induced EMF in loop in loop Getting the sign EMF in Faraday’s Law of Induction Define the loop and an area vector, A, who magnitude is the Area and whose direction normal to the surface. A The choice of vector A direction defines the direction of EMF with a right hand rule. Your thumb in A direction and then your fingers point to positive EMF direction. Lenz’s Law – easier way! The direction of any magnetic induction effect is such as to oppose the cause of the effect. ⇒ Convenient method to determine I direction Heinrich Friedrich Example if an external magnetic field on a loop Emil Lenz is increasing, the induced current creates a field opposite that reduces the net field. (1804-1865) Example if an external magnetic field on a loop is decreasing, the induced current creates a field parallel to the that tends to increase the net field. Incredible shrinking loop: a circular loop of wire with a magnetic flux is shrinking with time. In which direction is the induced current? (a) There is none. (b) CW. -
F = BIL (F=Force, B=Magnetic Field, I=Current, L=Length of Conductor)
Magnetism Joanna Radov Vocab: -Armature- is the power producing part of a motor -Domain- is a region in which the magnetic field of atoms are grouped together and aligned -Electric Motor- converts electrical energy into mechanical energy -Electromagnet- is a type of magnet whose magnetic field is produced by an electric current -First Right-Hand Rule (delete) -Fixed Magnet- is an object made from a magnetic material and creates a persistent magnetic field -Galvanometer- type of ammeter- detects and measures electric current -Magnetic Field- is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. -Magnetic Flux- is a measure of the amount of magnetic B field passing through a given surface -Polarized- when a magnet is permanently charged -Second Hand-Right Rule- (delete) -Solenoid- is a coil wound into a tightly packed helix -Third Right-Hand Rule- (delete) Major Points: -Similar magnetic poles repel each other, whereas opposite poles attract each other -Magnets exert a force on current-carrying wires -An electric charge produces an electric field in the region of space around the charge and that this field exerts a force on other electric charges placed in the field -The source of a magnetic field is moving charge, and the effect of a magnetic field is to exert a force on other moving charge placed in the field -The magnetic field is a vector quantity -We denote the magnetic field by the symbol B and represent it graphically by field lines -These lines are drawn ⊥ to their entry and exit points -They travel from N to S -If a stationary test charge is placed in a magnetic field, then the charge experiences no force. -
Faraday's Law Da
Faraday's Law dA B B r r Φ≡B •d A B ∫ dΦ ε= − B dt Applications of Magnetic Induction • AC Generator – Water turns wheel Æ rotates magnet Æ changes flux Æ induces emf Æ drives current • “Dynamic” Microphones (E.g., some telephones) – Sound Æ oscillating pressure waves Æ oscillating [diaphragm + coil] Æ oscillating magnetic flux Æ oscillating induced emf Æ oscillating current in wire Question: Do dynamic microphones need a battery? More Applications of Magnetic Induction • Tape / Hard Drive / ZIP Readout – Tiny coil responds to change in flux as the magnetic domains (encoding 0’s or 1’s) go by. 2007 Nobel Prize!!!!!!!! Giant Magnetoresistance • Credit Card Reader – Must swipe card Æ generates changing flux – Faster swipe Æ bigger signal More Applications of Magnetic Induction • Magnetic Levitation (Maglev) Trains – Induced surface (“eddy”) currents produce field in opposite direction Æ Repels magnet Æ Levitates train S N rails “eddy” current – Maglev trains today can travel up to 310 mph Æ Twice the speed of Amtrak’s fastest conventional train! – May eventually use superconducting loops to produce B-field Æ No power dissipation in resistance of wires! Faraday’s Law of Induction r r Recall the definition of magnetic flux is ΦB =B∫ ⋅ d A Faraday’s Law is the induced EMF in a closed loop equal the negative of the time derivative of magnetic flux change in the loop, d r r dΦ ε= −B∫ d ⋅= A − B dt dt Constant B field, changing B field, no induced EMF causes induced EMF in loop in loop Getting the sign EMF in Faraday’s Law of Induction Define the loop and an area vector, A, who magnitude is the Area and whose direction normal to the surface.