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.