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A bold capital J, current per unit cross-section.
Also known as: Current density, J field, Bold J
Current density is how much current crosses each square metre, and it is what actually determines whether a conductor melts — a thin wire and a thick one carrying the same amperes have very different densities. It is a vector, so it also carries the direction of flow.
Denotes electric current density: current per unit cross-sectional area, as a vector.
Contexts: Laboratory
Rather than total current, sets whether a conductor overheats, which is why cable ratings are given per unit area.
Contexts: Laboratory
Collides with the joule and with the moment of inertia, both also J.
Contexts: Laboratory
A bold capital letter J, a vertical stroke with a hooked foot curving left.