1. The problem statement, all variables and given/known data A length of Cu wire carries a current of 10 A uniformly distributed throughout its cross section. Calculate the energy density of (i) magnetic field (ii) the electric field at the surface of the wire. The wire diameter is 2.5 mm and its resistance per unit length is 3.3K/ km 2. Relevant equations I know that the energy density of magnetic field: U=uoI^2/16pi I know that the energy density of electric field: U=1/2*epsilon0I^2*R^2 3. The attempt at a solution Using the above equations I found that the magnetic energy density of the wire is 2.5 X10^-6 J/m^3 and the electric energy density of the wire is 48.2 J/m^3. How am I supposed to find the surface energy density(for both magnetic and electric) using the above values. Does it have anything to do with the radius?