# Finding magnitude of external field from two magnetic fields

1. Nov 2, 2008

### rosstheboss23

1. The problem statement, all variables and given/known data
I was wondering how would you determine the magnitude an external field needed to cancel two magnetic fields in two wires? In this instance the currents of the two wires are in opposite directions...so I know there is a repulsion force.
The currents in both wires are equal to 20 amps apiece
The wires are parallel to each other and are 0.019meters apart.

2. Relevant equations
Also I thought this would be useful B= (4piE-7)(I) divided by (2pie X r)

3. The attempt at a solution
When I tried to plug in the values for B I got 0.000210526 for the magnetic field in one wire. If I double this I get 0.000421053 for the total force of repulsion. Would this be the correct way of approaching the problem.

2. Nov 2, 2008

### Redbelly98

Staff Emeritus
No, just go with the 0.00021. That's the magnetic field due to one wire, at the location of the other wire.

3. Nov 2, 2008

### rosstheboss23

Thank you. I really appreciate your help.