# Homework Help: Finding current in a parralle wire

1. Feb 7, 2012

### monke

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

two long straight parallel wires seperated by 8.0 cm carry currents of equal magnitude but heading in opposite directions. Wires are perpendicular to the plane of the page. Point P is 2cm form wire 1. magnetic field at P = 0.01 T directed downward ( neg y direction). Calc Current in wire 1 and its direction.

2. Relevant equations

B= (μ.I)/2 pi r where mu not is 4pi X 10^-7 and r is the distance of the mag field from the wire.

3. The attempt at a solution

I tried using the given information and instead of solving for B solve for I (current) However my answer was incorrect.

Did i miss a step?

Thank You

2. Feb 8, 2012

### Fightfish

You have not been very clear in showing your entire approach.
However, I believe that the likely mistake that you made is overlooking the fact that the magnetic field of 0.01 T at P is the superposition of the individual magnetic fields from wires 1 and 2. Thus,
$$B_{p} = \frac{μ I}{2 \pi r_{1}} + \frac{μ I}{2 \pi r_{2}}$$
where $r_{1}$ denotes distance from wire 1 to P and $r_{2}$ denotes distance from wire 2 to P.

3. Feb 9, 2012

### monke

Thank you :) thats helps a ton