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Electromagnetic Wave In physics , ELECTROMAGNETIC RADIATION (EM RADIATION or EMR) refers to the waves (or their quanta, photons ) of the electromagnetic field , propagating (radiating) through spacetime, carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , (visible) light , ultraviolet , Xrays , and gamma rays . " Classically , electromagnetic radiation consists of ELECTROMAGNETIC WAVES, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum . The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave . The wavefront of electromagnetic waves emitted from a point source (such as a light bulb) is a sphere . The position of an electromagnetic wave within the electromagnetic spectrum could be characterized by either its frequency of oscillation or its wavelength [...More...]  "Electromagnetic Wave" on: Wikipedia Yahoo 

Faraday's Law Of Induction FARADAY\'S LAW OF INDUCTION is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF) —a phenomenon called electromagnetic induction . It is the fundamental operating principle of transformers , inductors , and many types of electrical motors , generators and solenoids . The MAXWELL–FARADAY EQUATION is a generalization of Faraday's law, and is listed as one of Maxwell\'s equations . CONTENTS * 1 History * 2 Faraday\'s law * 2.1 Qualitative statement * 2.2 Quantitative * 2.3 Maxwell–Faraday equation * 3 Proof of Faraday\'s law * 4 EMF for nonthinwire circuits * 5 Faraday\'s law and relativity * 5.1 Two phenomena * 5.2 Einstein\'s view * 6 See also * 7 References * 8 Further reading * 9 External links HISTORY A diagram of Faraday's iron ring apparatus [...More...]  "Faraday's Law Of Induction" on: Wikipedia Yahoo 

Lenz's Law LENZ\'S LAW (pronounced /ˈlɛnts/ ), named after the physicist Emil Lenz who formulated it in 1834, says: The direction of current induced in a conductor by a changing magnetic field due to Faraday\'s law of induction will be such that it will create a magnetic field that opposes the change that produced it. Lenz's law Lenz's law is shown by the negative sign in Faraday\'s law of induction : E = t , {displaystyle {mathcal {E}}={frac {partial Phi }{partial t}},} which indicates that the induced EMF ( E {displaystyle {mathcal {E}}} ) and the change in magnetic flux ( {displaystyle partial Phi } ) have opposite signs. It is a qualitative law that specifies the direction of induced current but says nothing about its magnitude [...More...]  "Lenz's Law" on: Wikipedia Yahoo 

Magnetic Potential The term MAGNETIC POTENTIAL can be used for either of two quantities in classical electromagnetism : the magnetic vector potential, A, (often simply called the vector potential) and the magnetic scalar potential, ψ. Both quantities can be used in certain circumstances to calculate the magnetic field . The more frequently used magnetic vector potential, A, is defined such that the curl of A is the magnetic field B. Together with the electric potential , the magnetic vector potential can be used to specify the electric field , E as well. Therefore, many equations of electromagnetism can be written either in terms of the E and B, or in terms of the magnetic vector potential and electric potential. In more advanced theories such as quantum mechanics , most equations use the potentials and not the E and B fields [...More...]  "Magnetic Potential" on: Wikipedia Yahoo 

Maxwell Stress Tensor The MAXWELL STRESS TENSOR (named after James Clerk Maxwell James Clerk Maxwell ) is a secondorder tensor used in classical electromagnetism to represent the interaction between electromagnetic forces and mechanical momentum . In simple situations, such as a point charge moving freely in a homogeneous magnetic field, it is easy to calculate the forces on the charge from the Lorentz force Lorentz force law . When the situation becomes more complicated, this ordinary procedure can become impossibly difficult, with equations spanning multiple lines. It is therefore convenient to collect many of these terms in the Maxwell stress tensor, and to use tensor arithmetic to find the answer to the problem at hand. In the relativistic formulation of electromagnetism, the Maxwell's tensor appears as a part of the electromagnetic stress–energy tensor which is the electromagnetic component of the total stress–energy tensor [...More...]  "Maxwell Stress Tensor" on: Wikipedia Yahoo 

Electromagnetic Induction ELECTROMAGNETIC or MAGNETIC INDUCTION is the production of an electromotive force (i.e., voltage) across an electrical conductor due to its dynamic interaction with a magnetic field . Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk Maxwell James Clerk Maxwell mathematically described it as Faraday\'s law of induction . Lenz\'s law describes the direction of the induced field. Faraday's law was later generalized to become the MaxwellFaraday equation, one of the four Maxwell\'s equations in James Clerk Maxwell's theory of electromagnetism. Electromagnetic induction Electromagnetic induction has found many applications in technology, including electrical components such as inductors and transformers , and devices such as electric motors and generators [...More...]  "Electromagnetic Induction" on: Wikipedia Yahoo 

Lorentz Force In physics (particularly in electromagnetism ) the LORENTZ FORCE is the combination of electric and magnetic force on a point charge due to electromagnetic fields . A particle of charge q moving with velocity V in the presence of an electric field E and a magnetic field B experiences a force F = q E + q v B {displaystyle mathbf {F} =qmathbf {E} +qmathbf {v} times mathbf {B} } (in SI units ). Variations on this basic formula describe the magnetic force on a currentcarrying wire (sometimes called Laplace force), the electromotive force in a wire loop moving through a magnetic field (an aspect of Faraday\'s law of induction ), and the force on a charged particle which might be travelling near the speed of light (relativistic form of the Lorentz force) [...More...]  "Lorentz Force" on: Wikipedia Yahoo 

Magnetic Flux In physics , specifically electromagnetism , the MAGNETIC FLUX (often denoted Φ or ΦB) through a surface is the surface integral of the normal component of the magnetic field B passing through that surface. The SI unit of magnetic flux is the weber (Wb) (in derived units: voltseconds), and the CGS unit is the maxwell . Magnetic flux Magnetic flux is usually measured with a fluxmeter, which contains measuring coils and electronics , that evaluates the change of voltage in the measuring coils to calculate the magnetic flux [...More...]  "Magnetic Flux" on: Wikipedia Yahoo 

Electromagnetic Waves (journal) PROGRESS IN ELECTROMAGNETICS RESEARCH is a peerreviewed open access scientific journal covering all aspects of electromagnetic theory and applications . It was established in 1989 as Electromagnetic Waves. The editorsinchief are Weng Cho Chew (University of Illinois at Urbana–Champaign ) and Sailing He ( Royal Institute of Technology Royal Institute of Technology ). Jin Au Kong was the founding editorinchief. ABSTRACTING AND INDEXINGThe journal is abstracted and indexed by the Science Citation Index Expanded , Current Contents , Inspec , Scopus , and Compendex . It is also a member of CrossRef CrossRef . According to the Journal Citation Reports , the journal had a 2011 impact factor of 5.298 [...More...]  "Electromagnetic Waves (journal)" on: Wikipedia Yahoo 

Magnetic Moment The MAGNETIC MOMENT of a magnet is a quantity that determines the torque it will experience in an external magnetic field . A loop of electric current , a bar magnet, an electron , a molecule , and a planet all have magnetic moments. The magnetic moment may be considered to be a vector having a magnitude and direction. The direction of the magnetic moment points from the south to north pole of the magnet (inside the magnet). The magnetic field produced by the magnet is proportional to its magnetic moment. More precisely, the term magnetic moment normally refers to a system's MAGNETIC DIPOLE MOMENT, which produces the first term in the multipole expansion of a general magnetic field. The dipole component of an object's magnetic field is symmetric about the direction of its magnetic dipole moment, and decreases as the inverse cube of the distance from the object [...More...]  "Magnetic Moment" on: Wikipedia Yahoo 

Gauss's Law For Magnetism In physics , GAUSS\'S LAW FOR MAGNETISM is one of the four Maxwell\'s equations that underlie classical electrodynamics . It states that the magnetic field B has divergence equal to zero, in other words, that it is a solenoidal vector field . It is equivalent to the statement that magnetic monopoles do not exist. Rather than "magnetic charges", the basic entity for magnetism is the magnetic dipole . (Of course, if monopoles were ever found, the law would have to be modified, as elaborated below.) Gauss's law for magnetism can be written in two forms, a differential form and an integral form. These forms are equivalent due to the divergence theorem . The name " Gauss's law for magnetism" is not universally used. The law is also called "Absence of free magnetic poles "; one reference even explicitly says the law has "no name" [...More...]  "Gauss's Law For Magnetism" on: Wikipedia Yahoo 

Poynting Vector In physics , the POYNTING VECTOR represents the directional energy flux (the energy transfer per unit area per unit time) of an electromagnetic field . The SI unit of the Poynting vector Poynting vector is the watt per square metre (W/m2). It is named after its discoverer John Henry Poynting who first derived it in 1884. :132 Oliver Heaviside :132 and Nikolay Umov :147 also independently discovered the Poynting vector [...More...]  "Poynting Vector" on: Wikipedia Yahoo 

Liénard–Wiechert Potential LIéNARD–WIECHERT POTENTIALS describe the classical electromagnetic effect of a moving electric point charge in terms of a vector potential and a scalar potential in the Lorenz gauge . Built directly from Maxwell\'s equations , these potentials describe the complete, relativistically correct, timevarying electromagnetic field for a point charge in arbitrary motion, but are not corrected for quantummechanical effects. Electromagnetic radiation Electromagnetic radiation in the form of waves can be obtained from these potentials. These expressions were developed in part by AlfredMarie Liénard in 1898 and independently by Emil Wiechert in 1900 [...More...]  "Liénard–Wiechert Potential" on: Wikipedia Yahoo 

Electric Potential An ELECTRIC POTENTIAL (also called the electric field potential or the electrostatic potential) is the amount of work needed to move a unit positive charge from a reference point to a specific point inside the field without producing any acceleration. Typically, the reference point is Earth or a point at Infinity, although any point beyond the influence of the electric field charge can be used. According to classical electrostatics , electric potential is a scalar quantity denoted by V, equal to the electric potential energy of any charged particle at any location (measured in joules ) divided by the charge of that particle (measured in coulombs ). By dividing out the charge on the particle a remainder is obtained that is a property of the electric field itself. This value can be calculated in either a static (timeinvariant) or a dynamic (varying with time) electric field at a specific time in units of joules per coulomb (J C−1), or volts (V) [...More...]  "Electric Potential" on: Wikipedia Yahoo 

Voltage VOLTAGE, ELECTRIC POTENTIAL DIFFERENCE, ELECTRIC PRESSURE or ELECTRIC TENSION (formally denoted ∆V or ∆U, but more often simply as V or U, for instance in the context of Ohm\'s or Kirchhoff\'s circuit laws ) is the difference in electric potential energy between two points per unit electric charge . The voltage between two points is equal to the work done per unit of charge against a static electric field to move the test charge between two points. This is measured in units of volts (a joule per coulomb ). Voltage Voltage can be caused by static electric fields, by electric current through a magnetic field , by timevarying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points [...More...]  "Voltage" on: Wikipedia Yahoo 

Electrical Resistance And Conductance The ELECTRICAL RESISTANCE of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is ELECTRICAL CONDUCTANCE, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction . The SI unit of electrical resistance is the ohm (Ω ), while electrical conductance is measured in siemens (S). An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its crosssectional area. All materials show some resistance, except for superconductors , which have a resistance of zero [...More...]  "Electrical Resistance And Conductance" on: Wikipedia Yahoo 