# Classical electromagnetism

**electrodynamicsclassical electrodynamicselectrodynamicclassicalclassical electromagnetic theoryclassical electromagneticclassical viewelectromagnetic field theoryelectromagnetic theoryelectromagnetism**

Classical electromagnetism or classical electrodynamics is a branch of theoretical physics that studies the interactions between electric charges and currents using an extension of the classical Newtonian model.wikipedia

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### Electric charge

**chargechargedelectrical charge**

Classical electromagnetism or classical electrodynamics is a branch of theoretical physics that studies the interactions between electric charges and currents using an extension of the classical Newtonian model.

An object with an absence of net charge is referred to as . Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.

### Quantum electrodynamics

**QEDquantum electrodynamicelectromagnetic**

For small distances and low field strengths, such interactions are better described by quantum electrodynamics.

In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics.

### John David Jackson (physicist)

**J. D. JacksonJohn David JacksonJ. David Jackson**

Fundamental physical aspects of classical electrodynamics are presented in many texts, such as those by Feynman, Leighton and Sands, Griffiths, Panofsky and Phillips, and Jackson.

A theoretical physicist, he was a member of the National Academy of Sciences, and is well known for numerous publications and summer-school lectures in nuclear and particle physics, as well as his widely-used graduate text on classical electrodynamics.

### Covariant formulation of classical electromagnetism

**special relativity formcan be rewrittenelectromagnetic displacement tensor**

Although the equation appears to suggest that the Electric and Magnetic fields are independent, the equation can be rewritten in term of four-current (instead of charge) and a single tensor that represents the combined Electromagnetic field (F^{\mu \nu})

The covariant formulation of classical electromagnetism refers to ways of writing the laws of classical electromagnetism (in particular, Maxwell's equations and the Lorentz force) in a form that is manifestly invariant under Lorentz transformations, in the formalism of special relativity using rectilinear inertial coordinate systems.

### Magnetic field

**magnetic fieldsmagneticmagnetic flux density**

where all boldfaced quantities are vectors: F is the force that a particle with charge q experiences, E is the electric field at the location of the particle, v is the velocity of the particle, B is the magnetic field at the location of the particle.

Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism.

### Coulomb's law

**coulombelectrostatic forceCoulomb force**

What is plain from this definition, though, is that the unit of E is N/C (newtons per coulomb).

This force and the law for quantifying it, represent one of the most basic forms of force used in the physical sciences, and were an essential basis to the study and development of the theory and field of classical electromagnetism.

### Differential equation

**differential equationsdifferentialsecond-order differential equation**

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).

PDEs can be used to describe a wide variety of phenomena in nature such as sound, heat, electrostatics, electrodynamics, fluid flow, elasticity, or quantum mechanics.

### Electromagnetic field

**electromagnetic fieldselectromagneticEMF**

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).

The behaviour of electric and magnetic fields, whether in cases of electrostatics, magnetostatics, or electrodynamics (electromagnetic fields), is governed by Maxwell's equations.

### Maxwell's equations

**equationsMaxwell equationselectromagnetic theory**

From Maxwell's equations, it is clear that ∇ × E is not always zero, and hence the scalar potential alone is insufficient to define the electric field exactly.

Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.

### Charge density

**charge distributionelectric charge densitycharge densities**

where is the charge density and is the vector that points from the volume element to the point in space where E is being determined.

In classical electromagnetic theory charge density is idealized as a continuous scalar function of position, like a fluid, and,, and are usually regarded as continuous charge distributions, even though all real charge distributions are made up of discrete charged particles.

### Electric potential

**electrical potentialelectrostatic potentialpotential**

A scalar function called the electric potential can help.

In electrodynamics, when time-varying fields are present, the electric field cannot be expressed only in terms of a scalar potential.

### Electromagnetic radiation

**electromagnetic waveelectromagnetic waveselectromagnetic**

Examples of the dynamic fields of electromagnetic radiation (in order of increasing frequency): radio waves, microwaves, light (infrared, visible light and ultraviolet), x-rays 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, which, in a vacuum, is commonly denoted c.

### Electromagnetic tensor

**electromagnetic field tensorfield strength tensorelectromagnetic field strength tensor**

Although the equation appears to suggest that the Electric and Magnetic fields are independent, the equation can be rewritten in term of four-current (instead of charge) and a single tensor that represents the combined Electromagnetic field (F^{\mu \nu})

In electrostatics and electrodynamics, Gauss's law and Ampère's circuital law are respectively:

### Electric field

**electricelectrostatic fieldelectrical field**

where all boldfaced quantities are vectors: F is the force that a particle with charge q experiences, E is the electric field at the location of the particle, v is the velocity of the particle, B is the magnetic field at the location of the particle.

Classical electromagnetism

### Electromagnetism

**electromagneticelectromagnetic forceelectromagnetics**

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).

In classical electrodynamics, electric fields are described as electric potential and electric current.

### Wheeler–Feynman absorber theory

**Wheeler–Feynman time-symmetric theoryadvanced waveWheeler-Feynman Time-symmetric theory**

Wheeler–Feynman absorber theory

The Wheeler–Feynman absorber theory (also called the Wheeler–Feynman time-symmetric theory), named after its originators, the physicists Richard Feynman and John Archibald Wheeler, is an interpretation of electrodynamics derived from the assumption that the solutions of the electromagnetic field equations must be invariant under time-reversal transformation, as are the field equations themselves.

### Leontovich boundary condition

Leontovich boundary condition

The Leontovich boundary condition is a classical electrodynamics boundary condition that relates to the tangential components of the electric E t and magnetic H t fields on the surface of well-conducting bodies.

### Jefimenko's equations

**time-dependent (retarded) generalizations of Coulomb's law and the Biot-Savart law**

For the fields of general charge distributions, the retarded potentials can be computed and differentiated accordingly to yield Jefimenko's equations.

These equations are the time-dependent generalization of Coulomb's law and the Biot–Savart law to electrodynamics, which were originally true only for electrostatic and magnetostatic fields, and steady currents.

### Retarded time

r q and v q are the position and velocity of the charge, respectively, as a function of retarded time.

The quantity is prominent in electrodynamics, electromagnetic radiation theory, and in Wheeler–Feynman absorber theory, since the history of the charge distribution affects the fields at later times.

### Liénard–Wiechert potential

**Liénard–Wiechert field**

Retarded potentials can also be derived for point charges, and the equations are known as the Liénard–Wiechert potentials.

Classical electromagnetism for the larger theory surrounding this analysis

### Theoretical physics

**theoretical physicisttheoreticaltheoretical physicists**

Classical electromagnetism or classical electrodynamics is a branch of theoretical physics that studies the interactions between electric charges and currents using an extension of the classical Newtonian model.

### Electric current

**currentcurrentselectrical current**

Classical electromagnetism or classical electrodynamics is a branch of theoretical physics that studies the interactions between electric charges and currents using an extension of the classical Newtonian model.

### Classical mechanics

**classicalNewtonianNewtonian physics**

### Length scale

**energy scaledistance scaleenergy**

The theory provides an excellent description of electromagnetic phenomena whenever the relevant length scales and field strengths are large enough that quantum mechanical effects are negligible.

### Quantum mechanics

**quantum physicsquantum mechanicalquantum theory**

The theory provides an excellent description of electromagnetic phenomena whenever the relevant length scales and field strengths are large enough that quantum mechanical effects are negligible.