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## Homework Statement

Calculate the magnetic and electric energy densities at the surface of a 3.0 mm diameter copper wire carrying a 15-A current

## Homework Equations

u

_{B}=.5[tex]\frac{B

^{2}}{\mu

_{0}}[/tex]

u

_{E}=.5[tex]\epsilon

_{0}[/tex]E

^{2}

R=[tex]\rho[/tex](L/A)

B=([tex]\mu

_{0}[/tex]I)/(2[tex]\pi[/tex]r)

[tex]\rho[/tex]=1.68 x 10^-8 ohm-meters

## The Attempt at a Solution

Okay, so finding the magnetic energy density isn't too difficult. My problem is with the electric energy density. I can use the area of the wire and the fact that it's copper to find the resistance and then use ohm's law to find the voltage. but then I get in this bind. E=V/d, but at the surface of the wire, d=0 so you get V/0 which kind of implies infinity and this agrees with my thoughts anyway. However, I feel like this doesn't really make any sense in terms of an electric energy density. Does some one see where the reasoning is going wrong and how I can make it right?