# Am I on the right track with Ampere's Law?

#### jumbogala

1. Homework Statement
A wire carries a current of 3 A in the downward direction. What is the magnetic field 2.0 cm away from the wire?

2. Homework Equations
∫B·dl = µ0I

3. The Attempt at a Solution
So I pick a circle with radius 2.0 cm to go around the wire, and get

B∫dl = µ0(3 A)

∫dl evaluates to 2pi(0.02 m).

So B = [µ0(3 A) ] / 2*pi*0.02 m?

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#### lalligagger

That works, however the Biot-Savart law is easier to apply here and actually reduces to a formula identical to what you have written in the last line in the case of a long straight wire. B=µ0I/2(pi)r

#### jumbogala

Thank you! I know the Biot-Savart law also works, I just wanted to make sure my concept of Ampere's Law was correct. =)

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