Help on magnetic field homework please

1. Feb 24, 2006

student85

Hello, I need help on understanding a concept in magnetic fields.
I have this homework were 4 long wires are parallel and viewed from on top they look as follows:

O - - - .2m - - - O
l l
l l
.2m .P .2m
l l
l l
O - - - .2m - - - O

So they form a square. What I need to find is the magnetic field in point P (center of square), magnitude and direction. The two wires on the right have electric currents emerging (going out of the page) and the two on the left have i going into the page. The values for all four of them are 5A.
I got the answer with me I just don't understand why the resulting magnetic field in P has its direction as going into the page.

Pleeease help. Any response is appreciated.

EDIT: for some reason the drawing doesn't come up right and two sets of lines appear together on the left side. Well it's supposed to be a square with each side being .2m

Last edited: Feb 24, 2006
2. Feb 24, 2006

dicerandom

FYI, you can get it to space correctly like this:
edit: well, the figure still didn't quite come out, but it's closer

Code (Text):

O - - - .2m - - - O
l                       l
l                       l
.2m       .P        .2m
l                       l
l                       l
O - - - .2m - - - O
I don't think that the magnetic field should point into the page though, I think it should point down. I'm just using the right hand rule here, stick your right thumb in the direction of the current and the direction that your fingers wrap around is the direction of the magnetic field. Using that method you should be able to see that the magnetic field generated by all of the wires is in the plane of the paper and the horizontal components will cancel out.

3. Feb 25, 2006

student85

Ok thanks. Yeah that is exactly what I thought.
Damn I misunderstood the book. Yes I'm right! Thanks anyway!