# Homework Help: Electric and Magnetic Field Relationship at the Surface of a Wire

1. Oct 30, 2012

### bmb2009

1. The problem statement, all variables and given/known data
A 0.60 m long circular tungsten wire with a radius of 0.05 m is connected to a DC power source resulting in a current of 0.65 A in the wire. Calculate the magnitude of the electric to magnetic field ratio at the surface of the wire. The resistivity of tungsten is 5.6 · 10-8 Ωm

2. Relevant equations

B(inside a wire) = μ*I/2∏R^2 * r where R = the radius of the wire and r = location within the wire radius... and since it is at the surface r=R.

Is that how you calculate the B field?

Also, I have no idea how to calculate the E field at the surface. I don't know how to relate resistivity into any of this. And does the I'm assuming the fact that it is a circle affects something but I don't know what.

I'm really lost on this problem so any response will be greatly appreciated!

3. The attempt at a solution

2. Oct 30, 2012

### TSny

Good on the B field except is r squared? For E, you can try applying Ohm's law to a short segment of the wire.

3. Oct 30, 2012

### bmb2009

Well since the r=R R/R^2 should reduce down to just R correct? and do you mind expanding on that? I really don't know how to do that :/

4. Oct 30, 2012

### bmb2009

Nevermind I got it! thanks though

5. Oct 30, 2012

### TSny

Oh, you were correct on the R factor. Good.