voolutugevuse

Voolutugevus, in English commonly called current density, is a vector field that describes the density and direction of electric current at each point inside a conductive medium. It is typically denoted by J and has units of amperes per square meter (A/m^2).

Definition and interpretation: J indicates how much current flows through a unit area perpendicular to the flow per unit time. The total current I crossing a given cross-section A is I = ∫_A J · dA. In a uniform wire, this reduces to I = J A. The direction of J corresponds to the conventional current flow.

Relations and properties: In ohmic media, J = σ E, where σ is the electrical conductivity and E is the electric field. More generally, J = σ̿ E when conductivity is anisotropic and must be treated as a tensor. The continuity equation ∇·J + ∂ρ/∂t = 0 expresses local charge conservation; in steady state, ∇·J = 0.

Importance and applications: Voolutugevus is central to understanding and predicting heating, efficiency, and performance in electrical circuits and devices. It informs design choices in power systems, integrated circuits, and materials research, and is a key variable in simulations such as finite element analyses of electrical fields and current distributions.

Measurement and visualization: Direct measurement of current density is challenging; engineers often infer J from magnetic field measurements, electrical impedance methods, or use imaging and scanning techniques in specialized research contexts. Numerical models commonly compute J from known E fields and material properties to assess performance and safety.

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