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**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