# Electromagnetic field

electromagnetic fieldselectromagneticEMFfieldelectro-magnetic fieldselectromagneticallyEM fieldFieldsmagnetic fieldAn EMF detector
An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.wikipedia
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### Field (physics)

fieldfieldsfield theory
An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.
This led physicists to consider electromagnetic fields to be a physical entity, making the field concept a supporting paradigm of the edifice of modern physics.

### Photon

photonslight quantalight
Experiments reveal that in some circumstances electromagnetic energy transfer is better described as being carried in the form of packets called quanta (in this case, photons) with a fixed frequency.
The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles).

### Electric charge

chargechargedelectrical charge
An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.
Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field.

In 1831, Michael Faraday, one of the great thinkers of his time, made the seminal observation that time-varying magnetic fields could induce electric currents and then, in 1864, James Clerk Maxwell published his famous paper A Dynamical Theory of the Electromagnetic Field.
It was by his research on the magnetic field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics.

### Lorentz force

magnetic forceLorentzLorentz force law
The way in which charges and currents interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law.
In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields.

### Quantum electrodynamics

QEDquantum electrodynamicelectromagnetic
This quantum picture of the electromagnetic field (which treats it as analogous to harmonic oscillators) has proven very successful, giving rise to quantum electrodynamics, a quantum field theory describing the interaction of electromagnetic radiation with charged matter.
Dirac described the quantization of the electromagnetic field as an ensemble of harmonic oscillators with the introduction of the concept of creation and annihilation operators of particles.

### Quantum optics

quantum electronicsquantum opticalquantum-optical
It also gives rise to quantum optics, which is different from quantum electrodynamics in that the matter itself is modelled using quantum mechanics rather than quantum field theory.
This led to the introduction of the coherent state as a concept which addressed variations between laser light, thermal light, exotic squeezed states, etc. as it became understood that light cannot be fully described just referring to the electromagnetic fields describing the waves in the classical picture.

electromagnetic waveelectromagnetic waveselectromagnetic
Although modern quantum optics tells us that there also is a semi-classical explanation of the photoelectric effect—the emission of electrons from metallic surfaces subjected to electromagnetic radiation—the photon was historically (although not strictly necessarily) used to explain certain observations.
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.

### History of electromagnetic theory

history of electricityhistory of electromagnetismelectricity
From a classical perspective in the history of electromagnetism, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner; whereas from the perspective of quantum field theory, the field is seen as quantized, being composed of individual particles.
Paul Dirac described the quantization of the electromagnetic field as an ensemble of harmonic oscillators with the introduction of the concept of creation and annihilation operators of particles.

### Speed of light

clight speedvelocity of light
In our everyday world, charged particles, such as electrons, move slowly through matter with a drift velocity of a fraction of a centimeter (or inch) per second, but fields propagate at the speed of light - approximately 300 thousand kilometers (or 186 thousand miles) a second.
The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed c with which electromagnetic waves (such as light) propagate through the vacuum is related to the distributed capacitance and inductance of the vacuum, otherwise respectively known as the electric constant ε 0 and the magnetic constant μ 0, by the equation

### Electromagnetism

electromagneticelectromagnetic forceelectromagnetics
The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction.
The electromagnetic force usually exhibits electromagnetic fields such as electric fields, magnetic fields, and light, and is one of the four fundamental interactions (commonly called forces) in nature.

### Classical electromagnetism

electrodynamicsclassical electrodynamicselectrodynamic
The behaviour of electric and magnetic fields, whether in cases of electrostatics, magnetostatics, or electrodynamics (electromagnetic fields), is governed by Maxwell's equations.
However, the theory of electromagnetism, as it is currently understood, grew out of Michael Faraday's experiments suggesting an electromagnetic field and James Clerk Maxwell's use of differential equations to describe it in his A Treatise on Electricity and Magnetism (1873).

### Electromagnetic tensor

electromagnetic field tensorfield strength tensorelectromagnetic field strength tensor
When an EM field (see electromagnetic tensor) is not varying in time, it may be seen as a purely electrical field or a purely magnetic field, or a mixture of both.
In electromagnetism, the electromagnetic tensor or electromagnetic field tensor (sometimes called the field strength tensor, Faraday tensor or Maxwell bivector) is a mathematical object that describes the electromagnetic field in spacetime.

### Quantum mechanics

quantum physicsquantum mechanicalquantum theory
It also gives rise to quantum optics, which is different from quantum electrodynamics in that the matter itself is modelled using quantum mechanics rather than quantum field theory.
A simpler approach, one that has been employed since the inception of quantum mechanics, is to treat charged particles as quantum mechanical objects being acted on by a classical electromagnetic field.

### Vector field

The first one views the electric and magnetic fields as three-dimensional vector fields.
Maxwell's equations allow us to use a given set of initial conditions to deduce, for every point in Euclidean space, a magnitude and direction for the force experienced by a charged test particle at that point; the resulting vector field is the electromagnetic field.

### Charge (physics)

chargechargescharged
Sources of electromagnetic fields consist of two types of charge – positive and negative.
Thus, for example, the gauge field of electromagnetism is the electromagnetic field; and the gauge boson is the photon.

### Near and far field

far fieldnear fieldnear-field
A changing electromagnetic field which is physically close to currents and charges (see near and far field for a definition of “close”) will have a dipole characteristic that is dominated by either a changing electric dipole, or a changing magnetic dipole.
The near field and far field are regions of the electromagnetic field (EM) around an object, such as a transmitting antenna, or the result of radiation scattering off an object.

Sometimes these high-frequency magnetic fields change at radio frequencies without being far-field waves and thus radio waves; see RFID tags.
Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects.

### Electric field

electricelectrostatic fieldelectrical field
The field can be viewed as the combination of an electric field and a magnetic field.
The total energy per unit volume stored by the electromagnetic field is

### Field strength

field intensityintensitymagnetic field intensity
The relative strengths and ranges of the four interactions and other information are tabulated below:
In physics, field strength means the magnitude of a vector-valued field (e.g., in volts per meter, V/m, for an electric field E). For example, electromagnetic field results in both electric field strength and magnetic field strength.

### Electromagnetic spectrum

spectrumspectrawhite light
EMR consists of the radiations in the electromagnetic spectrum, including radio waves, microwave, infrared, visible light, ultraviolet light, X-rays, and gamma rays.
During the 1860s James Maxwell developed four partial differential equations for the electromagnetic field.

### Dielectric heating

Changing electric dipole fields, as such, are used commercially as near-fields mainly as a source of dielectric heating.
Molecular rotation occurs in materials containing polar molecules having an electrical dipole moment, with the consequence that they will align themselves in an electromagnetic field.

### Plasma afterglow

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Afterglow plasma
The external electromagnetic fields that sustained the plasma glow are absent or insufficient to maintain the discharge in the afterglow.

### EMF measurement

detectorE.M.FElectromagnetic field measurements
Electromagnetic field measurements
EMF measurements are measurements of ambient (surrounding) electromagnetic fields that are performed using particular sensors or probes, such as EMF meters.

### Albert Einstein

EinsteinA. EinsteinEinstein, Albert
Charged particles can move at relativistic speeds nearing field propagation speeds, but, as Einstein showed, this requires enormous field energies, which are not present in our everyday experiences with electricity, magnetism, matter, and time and space.
Near the beginning of his career, Einstein thought that Newtonian mechanics was no longer enough to reconcile the laws of classical mechanics with the laws of the electromagnetic field.