Current is going into wire 1 and out of wire 2.
Wire 1 has a current density of 3 A/mm^2 and a diameter of 2 mm.
Wire 2 has a current density of 5 A/mm^2 and a diameter of 3 mm.
For part a I calculated the current in wire 3 to be 26 A.
Find the magnitude of the current density J_3 in wire 3. The diameter of wire 3 is 1.5 millimeters.
1 Answer

The area of wire 3 is pi*(1.5 * 10^3 mm)^2 /4 = 1.77 *10^6 m^2
since the current is 26 A the current density
J3 is 26 A/1.77 *10^6 m^2 = 1.47 * 10^7 A/m^2 or 14.7 A/mm^2