# Homework Help: Magnetic field due to wires.

1. Jun 30, 2011

### sphys4

1. The problem statement, all variables and given/known data
Because of the 2 wires in the figure,
For what value of the ratio I1/I2 is the magnetic field zero at the point A? point B? point C?

2. Relevant equations
http://tinypic.com/r/5otweg/7

3. The attempt at a solution
I honestly have no idea where to start with this problem, any help is appreciated!

I tried to upload the picture and it seems to not be working for me? My computer is really old so i dont know if its just not loading, if not here's the figure. http://tinypic.com/r/5otweg/7

2. Jul 1, 2011

### ideasrule

Assuming the bottom wire didn't exist, do you know how to calculate the magnetic field (both magnitude and direction) due to the first wire at A, B, and C? How about if the bottom wire was there, but the top one wasn't? The total magnetic field is just the vector sum of the contributions due to each wire.

3. Jul 1, 2011

### sphys4

Well then i would have to use B = ul/2pir?
So do i just find that for each of the wires and then add them together?