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  2. Maxwell's equations - Wikipedia

    en.wikipedia.org/wiki/Maxwell's_equations

    See below for a detailed description of the differences between the microscopic equations, dealing with total charge and current including material contributions, useful in air/vacuum; [note 6] and the macroscopic equations, dealing with free charge and current, practical to use within materials.

  3. Speed of electricity - Wikipedia

    en.wikipedia.org/wiki/Speed_of_electricity

    The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic wave traveling along (guided by) the cable. I.e., a cable is a form of a waveguide. The propagation of the wave is affected by the interaction with the material(s) in and surrounding the cable, caused by the presence of electric charge carriers ...

  4. Current (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Current_(mathematics)

    In mathematics, more particularly in functional analysis, differential topology, and geometric measure theory, a k-current in the sense of Georges de Rham is a functional on the space of compactly supported differential k-forms, on a smooth manifold M.

  5. Mathematical descriptions of the electromagnetic field

    en.wikipedia.org/wiki/Mathematical_descriptions...

    This seemingly violates causality in special relativity, i.e. the impossibility of information, signals, or anything travelling faster than the speed of light. The resolution to this apparent problem lies in the fact that, as previously stated, no observers can measure the potentials; they measure the electric and magnetic fields.

  6. List of common physics notations - Wikipedia

    en.wikipedia.org/wiki/List_of_common_physics...

    electric current: ampere (A) moment of inertia: kilogram meter squared (kg⋅m 2) intensity: watt per square meter (W/m 2) imaginary unit: unitless electric current: ampere (A) ^ Cartesian x-axis basis unit vector unitless current density: ampere per square meter (A/m 2) impulse

  7. Drift velocity - Wikipedia

    en.wikipedia.org/wiki/Drift_velocity

    The formula for evaluating the drift velocity of charge carriers in a material of constant cross-sectional area is given by: [1] =, where u is the drift velocity of electrons, j is the current density flowing through the material, n is the charge-carrier number density, and q is the charge on the charge-carrier.

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  9. Electromagnetism - Wikipedia

    en.wikipedia.org/wiki/Electromagnetism

    In the electromagnetic CGS system, electric current is a fundamental quantity defined via Ampère's law and takes the permeability as a dimensionless quantity (relative permeability) whose value in vacuum is unity. [32] As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in ...