Current Density Formula – Definition, Equations, Examples

Current Density Formula
Current Density Formula

Current Density Formula

In the field of electromagnetism, Current Density is the measurement of electric current (charge flow in amperes) per unit area of cross-section (m2). This is a vector quantity, with both a magnitude (scalar) and a direction.

J = I/A

J = current density in amperes/m2

I = current through a conductor, in amperes

A = cross-sectional area of the conductor, m2

Current Density Formula Questions:

1) A current of 6 mA is flowing through a copper wire that has an area of 4 mm2. What is the current density?

Answer: The current through the conductor is I = 6 mA = 0.006 amperes (or 6 x 10-3amps). The area of the wire is A = 4 mm2 = 0.004 m2 (or 4 x 10-3 m2). Use the equation for current density.

J = I/A

J = 0.006 amps/0.004 m2

J = 1.5 amps/m2

2) If 45 amperes of current is flowing through a battery with a given area of 8 m2, what is the current density?

Answer: The current, I = 45 amps and the area A = 8 m2.

J = I/A

J = 45 amps/8m2

J = 5.63 amps/m2

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