Electromagnetism Topics

2.17987190e-18 J
Rydberg Constant multiplied by Plancks constant and the speed of light.
2.9979e8 ms-1
Velocity of light in vacuo.
3.289841960368e15 Hz
Rydberg Constant multiplied by the speed of light.
376.73 Ohm
Impedance of free space.
Stefan-Boltzmann constant.
Permittivity of free space.
Adjacent Signal
A signal whose fundamental frequency falls outside the 3 dB IF bandpass of a receiver, but whose spectral sidebands have the potential of being linearly transferred into the baseband of a receiver and causing interference.
Air Core
The term used to describe inductors having no iron, steel, ferrite, or other magnetic core material.
Alnico Magnet
A magnet using aluminum, nickel, and cobalt in its construction.
Ampere′s Law
The line integral of the magnetic flux around a closed curve is proportional to the algebraic sum of electric currents flowing through that closed curve.
Angle of Arrival
A measure of the direction of propagation of electromagnetic radiation upon arrival at a receiver.
Annihilation Radiation
Electromagnetic radiation produced by the coalescence and mutual annihilation of a positron and an electron.
A length of wire or similar that radiates (such as a transmitting antenna) or absorbs (such as a radio antenna) radio waves.
Antenna Aperture
A surface, near or on an antenna, on which it is convenient to make assumptions regarding the field values for the purpose of computing fields at external points.
Antenna Array
A system of antennas coupled together to obtain directional effects, or to increase sensitivity.
Antenna Diversity
The technique of using more than one antenna to ensure that the received signal strength is always maximized.
Antenna Pattern
A representation, usually in the form of a polar or rectangular plotted graph, of the radiated field intensity of an antenna.
Antenna Regions
The distinction between electromagnetic fields far from, and those near to, the antenna.
A phenomenon observed in some materials in which complete magnetic moment cancellation occurs as a result of antiparallel coupling of adjacent atoms or ions.
Aperture Illumination
The field distribution, in amplitude and phase, over the antenna physical aperture.
Part of a circle.
Armature Air Gap
The air space between the stationary and rotating parts of a motor or generator, through which magnetic lines of force pass.
Asymmetric Capacitor
A capacitor where the two plates differ in surface area.
Authorised Carrier Frequency
A specific carrier authorized for use, from which the actual carrier frequency is permitted to deviate, solely because of frequency instability, by an amount not to exceed a given frequency tolerance.
Back Electromotive Force
The emf that opposes the normal flow of current in a circuit.
Back EMF
Abbreviation of Back Electromotive Force.
Back Lobe
The energy radiated from a directional antenna in a direction opposite to the axis of the main lobe.
Ball Lightning
A relatively rare form of lightning, consisting of a reddish, luminous ball, of the order of 0.3m in diameter, which may move rapidly along solid objects or remain floating in midair.
Barkhausen Effect
Phenomenon of short, sudden changes in the magnetism of a ferromagnetic substance occurring when the intensity of the magnetizing field is continuously altered.
Base Station
A focal point for data and communications.
BH Curve
A graph of the magnetic characteristics of ferromagnetic inductor cores. Flux density (B) is plotted against the magnetizing force (H).
A deliberate electromagnetic emission that carries intelligence through a modulation of one or more of its characteristics.
Cassegrain Antenna
An antenna used to achieve a highly directive, pencil beam emission with a plane wave front.
Occupying the same portion of the frequency spectrum.
Corner Reflector Antenna
A half-wave antenna with a reflector consisting of two flat metal surfaces meeting at an angle behind the radiator.
Cross Polarization
The polarization orthogonal to a reference polarization component.
Cyclotron Radius
Also known as Larmor Radius.
In microwave and common carrier systems, a measure of the noise power with reference to zero dBm at the Reference (zero) Transmission Level Point.
In microwave and common carrier systems, a measure of power with reference to zero dBm at the Reference Transmission Level Point.
In microwave and common carrier systems, circuit noise power measured with an instrument having psophometric weighting.
A weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative.
Diffraction Region
The space beyond the radio horizon which is shadowed from direct rays by the curvature of the earth or terrain irregularities or objects.
Directional Antenna
An antenna that radiates most effectively in only one direction.
Directive Gain
4π times the ratio of the radiation intensity in that direction to the total power radiated by the antenna.
Disruptive Discharge Coil
A Tesla oscillator which incorporates some form of spark gap switching device to discharge the primary capacitor(s) through the primary inductor.
The set of all allowable inputs for a function.
Earth Resonance
A theory stating that Earth possesses the properties of a massive LC circuit and can be resonated with a sufficiently powerful, properly tuned, grounded electrical oscillator.
Abbreviation of Electronic Counter-Countermeasures.
Abbreviation of Electronic Countermeasures.
Effective Aperture
A measure of the power extracted by an antenna from a passing electromagnetic wave.
Effective Earth Radius
The value used in place of the geometric radius of the earth to correct for atmospheric refraction when the index of refraction in the atmosphere changes linearly with height.
Effective Radiated Power
The product of the transmitter power in watts and the relative gain of a directional antenna as compared with a standard half-wave dipole.
Egg of Columbus
A novel demonstration apparatus used to explain the principal of the rotating magnetic field and the induction motor.
Electric Field
A field of forces that act on any electric charge placed within it. The stronger the field, the stronger the force that acts on the charge.
Electric Field Probe
A short antenna with a coaxial cable lead, used for the detection of high impedance E-field source signals over a very short range.
Electrodynamic Meter Movement
A meter movement using fixed field coils and a moving coil; usually used in ammeters and wattmeters.
The study of phenomena associated with charged bodies in motion and varying electric and magnetic fields.
A meter using an electrodynamic movement to measure an electric current.
A magnet formed by an inductor having current flow through it.
Electromagnetic Compatibility
The capability of different electrical systems to coexist in the electromagnetic environment without causing or being subjected to interference.
Electromagnetic Coupling
The transfer of electromagnetic energy from one circuit or system to another circuit or system.
Electromagnetic Energy
The energy stored in an electromagnetic field.
Electromagnetic Environment
The signal and noise complex within which communications-electronics devices are operated.
Electromagnetic Field
Electric and magnetic forces that exist in a physical volume.
Electromagnetic Force
A force with infinite range which acts between objects according to their charge.
Electromagnetic Induction
The production of a voltage in a coil because of a change in the number of magnetic lines of force passing through the coil.
Electromagnetic Interference
Any induced, radiated, or conducted electrical emission, disturbance, or transient that causes undesirable responses, degradation in performance, or malfunctions of any electrical or electronic equipment, device, or system.
Electromagnetic Pulse
The generation and radiation of a very narrow and very high-amplitude pulse of electromagnetic noise.
Electromagnetic Radiation
The emanation of an electromagnetic field from a source through space.
Electromagnetic Spectrum
Complete range of wavelengths for electromagnetic waves. These include infared, ultraviolet, and all other types of electromagnetic radiation, as well as visible light.
Electromagnetic Weapon
Any device which can produce an electromagnetic field of such intensity that targeted items of electronic equipment experience either a soft or hard kill.
Electromagnetically Induced Transparency
A technique that makes normally opaque substances transparent to light by applying another source of light, such as a laser beam, that interferes with the opaque substance′s absorption of light.
Electromagnetism Books
Lists all Electromagnetism Books in the Encyclopaedia
Electromagnetism Calculations
Lists all Electromagnetism Calculations in the Encyclopaedia
Electromagnetism Conversions
Lists all Electromagnetism Conversions in the Encyclopaedia
Electromagnetism Weblinks
Lists all Electromagnetism Weblinks in the Encyclopaedia
Electronic Counter-Countermeasures
Actions taken to insure friendly effective use of the electromagnetic spectrum despite the enemy's use of electronic warfare.
Electronic Countermeasures
Actions such as active electronic jamming taken to prevent, degrade or reduce effective use of the electromagnetic spectrum by an enemy, in electronic warfare.
Electronic Jamming
An electronic countermeasure that is the deliberate radiation, re-radiation, or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices, equipment, or systems.
Electronic Warfare
Military action involving the use of electromagnetic energy to determine, exploit, reduce or prevent hostile use of the electromagnetic spectrum and action which retains friendly use of the electromagnetic spectrum.
Pertaining to electricity at rest, such as charges on an object.
Electrostatic Deflection
The method of deflecting an electron beam by passing it between parallel charged plates mounted inside a cathode-ray tube.
Electrostatic Field
The field of influence between two differently charged bodies.
Electrostatic Force
Force experienced by stationary electrically charged particles in an electric field; the force which binds electrons to a nucleus in an atom.
Electrostatic Induction
A modification in the distribution of electric charge on one material under the influence of an electric charge on a nearby object.
Electrostatic Interactions
Attractions between opposite charges or repulsions between like charges that grow stronger as the charges become closer to each other.
Electrostatic Machine
A generator which produces an electric charge by friction or electrostatic induction.
Electrostatic Meter Movement
A meter movement that uses the electrostatic repulsion of two sets of charged plates.
Electrostatic Sensitivity
The degree to which a component or device is susceptible to damage by electrostatic discharge.
Electrostatic Stress
An electrostatic field acting on an insulator, which produces polarization in the insulator and causes electrical breakdown if raised beyond a certain intensity.
Electrostatic Unit
A unit of electric charge that exerts a force of 1 dyne on another unit of charge at a distance of 1 centimeter in a vacuum (cgs).
Small changes in the dimensions of a dielectric when placed in an electric field.
Abbreviation of Electromagnetic Compatibility.
Abbreviation of Electromagnetic Interference.
Abbreviation of Electromagnetic Pulse.
Abbreviation of Electrostatic Unit.
Faraday Cage
An earthed metallic wire or gauze screen enclosing electrical equipment to shield it from the influence of external electric fields.
Faraday Effect
The generation of a voltage by a coil when the coil is subjected to a changing magnetic field.
Faraday Rotation
The rotation of the plane of polarization of electromagnetic energy when it passes a substance influenced by a magnetic field that has a component in the direction of propagation.
Faraday Screen
An earthed wire screen placed in an equipment so as to prevent electrostatic but not electromagnetic coupling between components.
Faradays Laws of Electromagnetic Induction
Basic laws of electromagnetism relating to the operating principles of transformers, inductors, and many types of electrical motors and generators.
Material that has populations of atoms with opposing magnetic moments, the opposing moments are unequal and a spontaneous magnetization remains.
Ferrite Bead
A passive electric component used to suppress high frequency noise in electronic circuits, employing the mechanism of high dissipation of high frequency currents in a ferrite to give high frequency noise suppression.
Ferromagnetic Material
A highly magnetic material, such as iron, cobalt, nickel, or their alloys.
Permanent and large magnetizations found in some metals (e.g., Fe, Ni, and Co), which result from the parallel alignments of neighboring magnetic moments.
Flemings Left Hand Rule
A way of determining the direction of a force on a current carrying conductor in a magnetic field.
Flemings Right Hand Rule
A way of determining the direction of the induced emf of a conductor moving in a magnetic field.
Flux Density
The number of magnetic lines of force passing through a given area.
Fraunhofer Diffraction
Fraunhofer diffraction describes the diffraction pattern of electro-magnetic radiation observed in the far field from a slit or series of slits (i.e. grating).
Frequency Hopping
A spread spectrum communications technique in which a wireless transmitter and receiver are programmed to hop from frequency to frequency simultaneously.
Gauss Law for Magnetic Fields
The magnetic flux through a closed surface is zero; no magnetic charges exist.
Gauss′s Law
The electric flux through a closed surface is proportional to the algebraic sum of electric charges contained within that closed surface.
A machine that converts mechanical energy to electrical energy by applying the principle of magnetic induction.
Generator Rule
Also known as the Fleming′s Right Hand Rule this is a way of determining the direction of the induced emf of a conductor moving in a magnetic field.
Geomagnetic Field
The magnetic field observed in and around the Earth.
Ground Constants
The characteristics of the earth which affect surface propagation and ground reflection of an electromagnetic wave.
The natural period of revolution of a free electron in the earth′s magnetic field.
Also known as Larmor Radius.
A device for producing microwave energy that utilizes a strong axial magnetic field in a cavity resonator to produce azimuthal bunching of an electron beam.
Helical Antenna
An antenna constructed in the form of a helix.
H-Field Probe
A small Faraday screened loop antenna used for the detection of low impedance near field current sources.
High Frequency
The portion of the electromagnetic spectrum between 3000 kHz and 30,000 kHz.
High Power Effects
Interference effects that occur in the presence of strong signals.
High-Field Emission
The discharge of electrons from the surface of a material subjected to a strong electric field.
Induced Electromotive Force
Voltage induced in a conductor in a varying magnetic field.
The property of an electric circuit to store magnetic energy when carrying a current.
The act or process of producing voltage and current by the relative motion of a magnetic field across a conductor.
Induction Field
The electromagnetic field that is produced about an antenna when current and voltage are present on the same antenna.
Induction Heating
Heating by combined electrical resistance and hysteresis losses induced by subjecting a metal to varying magnetic field surrounding a coil carrying alternating current.
Induction Losses
The losses that occur when the electromagnetic field around a conductor cuts through nearby metallic objects and induces a current into that object.
Inductive Coupling
Coupling of two coils by means of magnetic lines of force.
Inductive Load
Load whose voltage and current are out-of-phase.
Inductive Reactance
The opposition to the flow of an alternating current caused by the inductance of a circuit, expressed in ohms.
Inductively Coupled Discharge
A plasma created by applying an oscillating, radiofrequency potential to an inductive coil.
A magnetic device that stores energy in a magnetic field produced by flowing current.
Intensity of Magnetism
This is the magnetic moment per unit volume of a magnet.
Isotropic Antenna
A hypothetical loss-less antenna which radiates or receives energy equally in all directions.
Abbreviation of kilogauss.
Equal to 1000 gauss or 0.1 tesla.
Larmor Radius
The radius of the path of a charged particle moving in a magnetic field and transverse to the field lines.
Law of Magnetism
Like poles repel; unlike poles attract.
Lorentz Force
The force on a charged particle moving in a magnetic field.
Lossy Medium
A medium which absorbs or scatters radiation passing through it.
Low Frequency
The portion of the electromagnetic spectrum between 30 kHz and 300 kHz.
A magnet is a device that produces a magnetic field.
A magnet or a material which is capable of being magnetized.
Magnetic Amplifier
An electromagnetic device that uses one or more saturable reactors to obtain a large power gain.
Magnetic Confinement
Method of containing a plasma or charged particles in a finite region using magnetic fields.
Magnetic Declination
The angle between magnetic north and true north at a given point on the Earth′s surface.
Magnetic Equator
The line through those points on the earth′s surface at which magnetic dip is zero.
Magnetic Field
The region in which the magnetic forces created by a permanent magnet or by a current-carrying conductor or coil can be detected.
Magnetic Field Intensity
The force that drives the generation of rnagnetic flux in a material. it is also called magnetizing force and can be produced by the application of an electric current.
Magnetic Field Probe
A small Faraday screened loop antenna used for the detection of low impedance near field current sources.
Magnetic Field Strength
The intensity of an externally applied magnetic field.
Magnetic Flux
The surface integral of the product of the permeability of the medium and the magnetic field intensity normal to the surface.
Magnetic Flux Density
The magnetic flux density is the product of field intensity and the permeability of the medium.
Magnetic Hysteresis
When a ferromagnetic material is placed in an alternating magnetic field, the flux density (B) lags behind the magnetizing force (H) that causes it. The area under the hysteresis loop is the hysteresis loss per cycle, and is high for permanent magnets and low for high-permeability, low-loss magnetic materials.
Magnetic Induction
Generating a voltage in a circuit by the creation of relative motion between a magnetic field and the circuit.
Magnetic Lens
Circular electro-magnets capable of projecting a precise circular magnetic field in a specified region.
Magnetic Lines of Force
Imaginary lines used for convenience to designate the direction in which magnetic forces are acting as a result of magnetomotive force.
Magnetic Moment
This is the couple exerted on a magnet placed at right angles to a uniform field with unit magnetic flux density.
Magnetic Monopole
A hypothesized, isolated magnetic pole.
Magnetic Permeability
This indicates the ability of a material to support magnetic lines of flux. The magnetic permeability of a material is the product of the relative permeability of that material and the permeability of free space. The relative permeability of most nonferrous materials is near unity.
Magnetic Pole
One end of a magnet; analogous to an electric charge.
Magnetic Pressure
The pressure which a magnetic field is capable of exerting on a plasma; equal to the magnetic energy density.
Magnetic Saturation
The upper limit of the abilIty of a ferromagnetic material to carry flux.
Magnetic Susceptibility
The proportionality constant between the magnetization and the magnetic field strength.
The property possessed by certain materials by which these materials can exert mechanical force on neighboring masses of magnetic materials and can cause currents to be induced in conducting bodies moving relative to the magnetized bodies.
The total magnetic moment per unit volume of material.
Of or pertaining to electricity produced by or associated with magnetism.
Magnetohydrodynamic Waves
Material waves in an electrically conducting fluid in the presence of a magnetic field.
Academic discipline which studies the dynamics of electrically-conducting fluids and their interactions with magnetic fields.
The change of size and/or shape of a ferromagnetic material due to the application of a magnetic field.
Abbreviation of Microwave Amplification by Stimulated Emission of Radiation.
Maximum Effective Aperture
With respect to any antenna, the ratio of the square of the incident voltage to four times the product of the incident power density and antenna radiation resistance.
Maxwell Equations
Describe the relationship between electric and magnetic fields at any point in space as a function of charge density and electric current at such a point.
Medium Frequency
The portion of the electromagnetic spectrum between 300 kHz and 30,000 kHz.
Meteor Burst Communications
A telecommunication technique which uses meteor activity in the ionosphere as a mechanism for reflecting short data transmissions from field sites to a base station.
Microwave Amplification by Stimulated Emission of Radiation
Emission of energy stored in a molecular or atomic system by a microwave power supply is stimulated by the input signal.
Mutual Inductance
A circuit property existing when the relative position of two inductors causes the magnetic lines of force from one to link with the turns of the other.
A point or line on a vibrating structure that remains stationary.
Non-Ionizing Radiation
Radiation without enough energy to remove tightly bound electrons from their orbits around atoms.
Norton Surface Wave
The ground-wave component of a space wave resulting from refraction of a portion of the reflected-wave component at the Earth-atmosphere interface and induction of electrical currents in the ground.
Occupied Bandwidth
The frequency bandwidth such that, below its lower and above its upper frequency limits, the mean powers radiated are each equal to 0.5% of the total mean power radiated by a given emission.
Paramagnetic Material
A material having a permeability slightly greater than 1.
A relatively weak form of magnetism that results from the independent alignment of atomic dipoles (magnetic) with an applied magnetic field.
Path Loss
The power attenuation of a signal over the path between a transmitting antenna and a receiving antenna, due to all causes.
A frequency band used in radar extending approximately from 225 to 390 megacycles per second.
Pencil Beam
Emission, from an antenna, having the form of a narrow conical beam.
Permanent Magnet
A magnet that retains its magnetism after removal of the magnetizing force.
Phased Array Antenna
An array antenna whose beam direction or radiation pattern is controlled primarily by the relative phases of the excitation coefficients of the radiating elements.
Power Flux Density
In radio wave propagation, the power crossing unit area normal to the direction of wave propagation.
Power Surface Density
Radiant power incident on a small sphere, divided by the cross-sectional area of that sphere.
Propagation Loss
The attenuation of signals passing between two points in a transmission path.
Propagation Path
The route by which a signal, or a portion of a signal, travels from transmitting antenna to receiving antenna. Possible paths include the direct path, reflected path, skywave path, refracted path, etc.
Pulse Modulated Field
An electromagnetic field produced by the amplitude modulation of a continuous wave carrier by one or more pulses.
A frequency band used in radar extending approximately from 36 to 46 kilomegacycles.
Quasineutral Plasma
A plasma in which positive and negative charges are present in approximately equal numbers, so that there are no strong net electric fields.
Radiation Transport
The field of nuclear science dealing with the prediction and measurement of the movement of electromagnetic radiation or particles through matter.
Radio Frequency Heating
A process for heating plasma by transferring energy to ions or electrons using waves generated by an external oscillator at an appropriate frequency, and propagated into the plasma.
Radio Interference
The interference with radio reception caused by a system.
Radio Interference Suppression
The methods employed to minimize radio interference.
Radio Waves
Electromagnetic radiation in the region of the spectrum smaller than about 3 x 108Hz and wavelengths greater than about 1 m.
Relative Magnetic Permeability
The ratio of the magnetic permeability of some medium to that of a vacuum.
Residual Induction
This is the point at which the hysteresis loop crosses the B axis at zero magnetizing force, and represents the maximum flux output from the given magnet material.
Residual Magnetism
Magnetism remaining in a substance after removal of the magnetizing force.
Also called Remanence.
A band of radio frequencies extending from 1550 to 5200 MHz.
Self Induction
The production of a counter electromotive force in a conductor when its own magnetic field collapses or expands with a change in current in the conductor.
Abbreviation of Super High Frequency.
A portion of the energy from a directional antenna, radiated in a direction other than the boresight axis.
Sky Wave
The space-wave component of a radio transmission that reaches the receiver by reflection from the ionosphere.
Space Wave
Radio waves that travel directly from the transmitter to the receiver and remain in the troposphere.
Spatial Power Density
The net power in a given cross sectional area of a propagating medium. Convenient units are watts (or dBm) per square meter. Spatial power density is independent of frequency.
Spurious Emission
Far-field electromagnetic radiation transmitted on a frequency outside the bandwidth required for satisfactory transmission of the required waveform.
A separate analog or digital signal carried on a main radio transmission, which may carry extra information such as voice or data.
Submillimeter Wave
The portion of the electromagnetic spectrum between 300 GHz and 1 THz, also known as microwave.
Superconducting Magnets
An electromagnet whose coils are made of a type II superconductor with a high transition temperature and extremely high critical field.
Temporary Magnet
Material which has magnetic properties when being brought near a magnetic field, but which loses these properties when the field is removed.
Tesla Antenna
A form of wireless antenna or wave launching structure developed by Nikola Tesla.
Tesla Coil
An electrical oscillator developed by Nikola Tesla which produces high voltage, radio frequency alternating electric current.
Tesla Coil Transmitter
A Tesla coil configured specifically for the purpose of wireless transmission of electrical energy using either of two ground-based methods.
Tesla Effect
The wireless transmission of electrical energy between a Tesla coil transmitter and a Tesla receiving transformer by the means of electrical currents.
Tesla Receiving Transformer
A grounded resonance transformer specifically intended for the reception of energy transmitted by a Tesla coil transmitter.
Travelling Wave Tube
Electron tube in which a beam of electrons interacts continuously with the electric field of an electromagnetic wave traveling in a helix to produce amplification at ultra-high frequencies and above.
Tropospheric Ducting
The propagation of radio signals above 30 Mhz via bending and ducting along weather fronts in the lowest layer of the Earth′s atmosphere.
Abbreviation of Ultra Low Frequency.
Ultra Low Frequency
The portion of the electromagnetic spectrum below 3 Hz.
Van de Graaff Generator
An electrostatic generator which employs a system of conveyor belt and spray points to charge an insulated electrode to a high potential.
the frequency band from 46,000 to 56,000Mhz employed in radar.
Velocity Modulation
Modification of the velocity of an electron beam by the alternate acceleration and deceleration of electrons.
Vertical Polarization
An electromagnetic emission is vertically polarized when its electric field (E vector) is perpendicular to the plane of the earth.
Villari Effect
The change in magnetic properties of a ferromagnetic material in response to the presence of stress in the ferromagnetic material.
Voltage Standing Wave Ratio
In a waveguide, the ratio of the electric field (voltage) at a maximum point to that of an adjacent minimum point.
Wave Antenna
Same as a Beverage Antenna.
A rectangular, circular, or elliptical metal pipe designed to transport electromagnetic waves through its interior.
Waveguide Mode of Operation
Any particular field configuration in a waveguide that satisfies the boundary conditions.
Waveguide Post
A rod of conductive material used as impedance changing devices in waveguides.
Waveguide Screw
A screw that projects into a waveguide for the purpose of changing the impedance.
A radiofrequency electromagnetic signal generated by some lightning discharges.
the frequency band from 5200 to 10,900Mhz employed in radar.
Zenneck Surface Wave
A low frequency transverse magnetic surface wave that travels along the interface between the ground and the air, in which the propagating energy does not radiate into space but is concentrated near the guiding surface.

See also: Oersted, Hans Christian.

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Subjects: Mechanical Engineering Physics