# Electric field density at the surface of a current carring wire

1. Mar 5, 2009

### cuttlefish

1. The problem statement, all variables and given/known data
Calculate the magnetic and electric energy densities at the surface of a 3.0 mm diameter copper wire carrying a 15-A current

2. Relevant equations
uB=.5$$\frac{B2}{\mu0}$$
uE=.5$$\epsilon0$$E2
R=$$\rho$$(L/A)
B=($$\mu0$$I)/(2$$\pi$$r)
$$\rho$$=1.68 x 10^-8 ohm-meters
3. 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?

2. Mar 5, 2009

### cuttlefish

whoa....okay the equations got screwed up there. Hope you can understand them...B^2 is obviously the one in magnetic energy density, mu sub zero, E^2. Sorry about that folks.

3. Mar 5, 2009

### cuttlefish

I've just realized that the same problem comes up with my magnetic field. So. Basically I have no idea what I'm doing and am in need of desperate help.