Current density is a vector physical quantity equal to the ratio of the electric current passing through an elementary surface located perpendicular to the direction of charge movement to its area.

Current density is measured in Amperes per square meter (A/m²) or Amperes per square centimeter (A/cm²), depending on the unit system. In the SI system, current is measured in amperes. Therefore, current density is measured in A/m².

It is denoted by the Latin letter “j.”

where I is the current passing through the cross-sectional area of the conductor with an area of S.

Current density is an important physical quantity as it allows determining the electric field around the conductor and describes the dependence of current on the size of the conductor. High values of current density can lead to the heating of the conductor and, ultimately, to material damage.

Current density also plays a crucial role in electrical engineering and electronics. For instance, in electric circuits, it helps to calculate the resistance of circuit elements and determine the power consumed by the circuit elements. In electronic devices, it aids in calculating the efficiency of transistors and other electronic components.