# Homework Help: Proof involving Ampere's Law

1. Apr 6, 2010

### alanthreonus

1. The problem statement, all variables and given/known data

Ampere's Law states $$\int _C \vec{B} \cdot \vec{dr} = \mu_0 \ I$$ .

By taking C to be a circle with radius r, show that the magnitude B = |B| of the magnetic field at a distance r from the center of the wire is $$B = \frac{\mu_0}{2 \pi} \ \frac{I}{r}$$

3. The attempt at a solution

I really don't know where to start. I don't know what the components of B are, so I don't know how I'm supposed to compute this integral.

Last edited: Apr 6, 2010
2. Apr 6, 2010

### espen180

What do you know about the B-field at a distace r from the wire, magnitude-wise? How can you use this knowledge in computing the integral?