Magnetic fields and conduction

[jalen]

1. Homework Statement

12.5A, 3.1x10^-5

2. Homework Equations

How far from a long conductor passing a current of 12.5A is the magentic field of strength 3.1x10^-5T?

3. The Attempt at a Solution

B= uI/2(pi)r

r=uI/2(pi)B
=(4pi)(12.5A)/ 2(pi)(3.1x10^-5T)
= 8.1x10^5m

 

[Snazzy]

u_0 isn't 4 pi.