Homework Help: Finding Magnetic Field at Point P

1. Oct 26, 2008

0338jw

1. The problem statement, all variables and given/known data
Two long thin parallel wires 13 cm apart carry 25A currents in the same direction. Determine the magnetic fild at point P 12 cm from one wire and 5 cm from the other.

2. Relevant equations
B=mu/2pi * I/r

3. The attempt at a solution

I have already solved this problem, and I have the answers. The problem is I wasn't too specific when doing it and now cant figure out for the life of me how I got the angle I used! when I use ratios like (.12/.13) instead of Cos theta it works out opposite, for the other current carrying wire. How do I know what is theta? I remember vaguely doing something like 90-theta then doing cos/sin of that to find the xy components. Helping me with this would mean a LOT to me guys. I checked the book for similar examples, none. Only ones where forces are all x or all y with no components.

EDIT: I have the angles now, but I'm still unsure which to use for which current carrying wire. I have 67.4 and 22.6. Do I do 90 - the angle I get fr each current carrying wire since the B field is perpendicular?

Last edited: Oct 26, 2008
2. Oct 28, 2008

alphysicist

Hi 0338jw,

Are you referring to finding the components of each field? That would depend on the angle that the line to point P makes with the coordinate axes. Are the point and the two wires all in a line, or are they arranged somehow else? Can you upload a picture, or provide more description?