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current density

The current density (J) is a measure of the number of charge carriers in a conductor. By definition, it is the current in amperes

(A) that passes through a given conductor cross-section (A). If the conductor cross-section becomes larger, the current density decreases; if the conductor cross-section becomes smaller, the current density increases, since the same current flows through a smaller cross-section

. Thecurrent density is thus calculated from the ratio of the current intensity in amperes (A) to the conductor cross-section in square millimetres.

This relationship applies to direct current and low-frequency alternating current, in which the distribution of the charge carriers is uniform. As soon as alternating current has a low frequency, such as the mains frequency, the skin effect occurs, which presses the current overproportionally to the conductor surface and thus ensures an uneven distribution.

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Englisch: current density
Updated at: 07.04.2015
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