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  2. Current density - Wikipedia

    en.wikipedia.org/wiki/Current_density

    In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.

  3. Probability current - Wikipedia

    en.wikipedia.org/wiki/Probability_current

    As in those fields, the probability current (i.e. the probability current density) is related to the probability density function via a continuity equation. The probability current is invariant under gauge transformation. The concept of probability current is also used outside of quantum mechanics, when dealing with probability density ...

  4. List of electromagnetism equations - Wikipedia

    en.wikipedia.org/wiki/List_of_electromagnetism...

    Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal nĚ‚, d is the dipole moment between two point charges, the volume density of these is the polarization density P.

  5. Maxwell's equations - Wikipedia

    en.wikipedia.org/wiki/Maxwell's_equations

    The equations introduce the electric field, E, a vector field, and the magnetic field, B, a pseudovector field, each generally having a time and location dependence. The sources are the total electric charge density (total charge per unit volume), ρ, and; the total electric current density (total current per unit area), J.

  6. Skin effect - Wikipedia

    en.wikipedia.org/wiki/Skin_effect

    Regardless of the driving force, the current density is found to be greatest at the conductor's surface, with a reduced magnitude deeper in the conductor. That decline in current density is known as the skin effect and the skin depth is a measure of the depth at which the current density falls to 1/e of its value near the surface. Over 98% of ...

  7. Butler–Volmer equation - Wikipedia

    en.wikipedia.org/wiki/Butler–Volmer_equation

    The upper graph shows the current density as function of the overpotential η . The anodic and cathodic current densities are shown as j a and j c, respectively for α=α a =α c =0.5 and j 0 =1mAcm −2 (close to values for platinum and palladium). The lower graph shows the logarithmic plot for different values of α (Tafel plot).

  8. Mathematical descriptions of the electromagnetic field

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

    These equations are inhomogeneous versions of the wave equation, with the terms on the right side of the equation serving as the source functions for the wave. As with any wave equation, these equations lead to two types of solution: advanced potentials (which are related to the configuration of the sources at future points in time), and ...

  9. Electric current - Wikipedia

    en.wikipedia.org/wiki/Electric_current

    For negative charges, the sign of the current density is opposite to the velocity of the charges. [2]: 749 In SI units, current density (symbol: j) is expressed in the SI base units of amperes per square metre. [4]: 22 In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform.