Answer
We can rank the three rods according to the current density:
$1 = 2 \gt 3$
Work Step by Step
In part (a), we ranked the rods according to the magnitude of the electric field within
them as follows:
$1 = 2 \gt 3$
We can write a general expression for the current density:
$J = \sigma E$
$\sigma$ is a characteristic of the copper which is the same for all rods.
We can see that there is a higher magnitude of current density when there is a higher magnitude of electric field.
We can rank the three rods according to the current density:
$1 = 2 \gt 3$
