A wire of circular cross$-$section carries current density that is not uniform but varies with distance from the center as

j$($r$)=$A$($r$)/($R$)$

for radius r in the range AR$=5\mathrm{.}7$mm$0.$ Here, A is a constant with units of amperes per square meter, and the radius of the wire is R$=5\mathrm{.}7$mm$.$