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

[jumbogala]

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?

Homework Equations

∫B·dl = µ₀I

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?

 

[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. =)