What exactly is the physical significance or meaning of Current density?

The formula $J=\frac{I}{A}$ is one thing but what does this represent, I am unable to visualize it or feel it.

We have already defined current as charge flowing through a cross section per unit time as current but now what does current density mean?

For example, while deriving the formula for magnetic field due to a infinite sheet, I came across the term take current per unit area as $J$, what information does this give me? I am really confused regarding current density and I don't have any intuitive feeling regarding it. How should I think about it? Please help.

  • 1
    $\begingroup$ Related : Surface Current Density. From @Andrew Steane's answer : "Current density" (without any other adjectives) means "charge passing a plane per unit time, per unit area of the plane". "Surface current density" means "amount of charge in a thin sheet of current passing a given place, per unit time, per unit length across the wide dimension of the sheet of current". $\endgroup$
    – Frobenius
    Sep 4, 2021 at 9:11
  • $\begingroup$ @Frobenius Thanks, understanding it in terms on charge is a bit helpful now. $\endgroup$ Sep 4, 2021 at 9:19

2 Answers 2


The current is due to moving charges (electrons).

Imagine 9 electrons are moving into the paper (or screen)

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Diagram A has a low current density, diagram B has a higher current density.

  • $\begingroup$ Are both currents same? $\endgroup$ Nov 8, 2022 at 12:28

Visualize a cross-section through an electric wire. The current density is the current divided by the cross-section's area. Increasing this area allows for a greater current, which is why a wire's resistance is inversely proportional to that area.

  • $\begingroup$ I approved your nice answer. $\endgroup$
    – Sebastiano
    Sep 5, 2021 at 12:36

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