Electric current is the flow of electric charge through a material. It is the rate at which electric charge flows past a point in a circuit. The flow of electric charge is typically carried by electrons, which are negatively charged particles.
The SI unit for current is the coulomb per second, or the ampere (A), which is an SI base unit:
1 ampere = 1A = 1 coulomb per second = 1 C/s.
Electric current density is a measure of the flow of electric charge per unit area of a conductor. It is defined as the amount of electric current passing through a unit area perpendicular to the direction of current flow.
The formula for electric current density is:
J = I / A
where J is the electric current density (in amperes per square meter), I is the current flowing through the conductor (in amperes), and A is the cross-sectional area of the conductor (in square meters).
Electric current density can be a useful parameter for analyzing the behavior of electrical circuits, particularly in situations where the cross-sectional area of the conductor varies or where there are localized sources or sinks of current. It can also be used in materials science and other fields to analyze the behavior of conductive materials under different conditions.
In practice, electric current density can be measured using a variety of techniques, such as magnetic field measurements, Hall effect sensors, or contact probes that measure the voltage drop across a small region of the conductor.