There is a cylindrical copper wire with radius $0\mathrm{.}321$ mm and length of $0\mathrm{.}5$ m connected to a cylindrical aluminum wire of radius $0\mathrm{.}287$ mm and length of $0\mathrm{.}5$ m $.$ The resistivity of copper is $1\mathrm{.}72{10}^{-8}m$ and the resistivity of aluminum is $2\mathrm{.}75{10}^{-8}m.$ The current density in the copper wire is $1\mathrm{.}93{10}^7\frac{A}{m^2}.$