When finding Magnetic Field between two wires

[mistermill]

Homework Statement

11. Two parallel conductors, 1.0 cm apart, each carry 10 A of current in opposite directions. What is the magnetic field strength at the midpoint between these wires?

Homework Equations

B = μI/ 2πr

The Attempt at a Solution

I know that the magnetic field is doubled because the currents are in opposite directions.

Should r = 0.01 m or 0.005 m?

Is the r the distance between the two wires? I thought that r is the perpendicular distance from the wire to the point of field measurement, so that would mean 0.005 m.

I think the answer in my book is wrong, because it has r = 0.01 m.

Please advise.

 

[TSny]

Hi, mistermill.

You are correct. r is the perpendicular distance from the wire to the field point. So, r = .005 m for each current.