Assume that A (SI unit: m ) is a small surface centered at a given point M and orthogonal to the motion of the charges at … 展开

Current density is important to the design of electrical and electronic systems.
Circuit performance depends strongly upon the designed current level, and the current density then is determined by the dimensions of th… 展开

Charge carriers which are free to move constitute a free current density, which are given by expressions such as those in this section.
Electric current is a coarse, average quantity that tell… 展开

Since charge is conserved, current density must satisfy a continuity equation. Here is a derivation from first principles.
The net flow out of some volume V (which can have an arbitrary shape but fixed for the calculation) … 展开

In electrical wiring, the maximum current density (for a given temperature rating) can vary from 4 A⋅mm for a wire with no air circulation around it, to over 6 A⋅mm for a wire in free air. Regulations for building wiring list … 展开

• Hall effect
• Quantum Hall effect
• Superconductivity
• Electron mobility
• Drift velocity… 展开