# Magnetic Field vectors

1. May 1, 2005

### dsandhu

I have racked my brain for the past two hours and I can't figure this out. If any one can help me with, please do.

Two long parallel wires 6.00 cm apart carry 19.5 A currents in the same direction. Determine the magnetic field strength at a point 12.0 cm from one wire and 13.4 cm from the other. (Hint: Make a drawing in a plane containing the field lines, and recall the rules for vector addition.)

I found the magnetic field for each of the wires seperately using B = Mo(I)/ r

but I cannot understand what the "vectors" have to do with the problem.

2. May 1, 2005

### Staff: Mentor

The magnetic field is a vector: direction matters! The magnitude of the magnetic field surrounding a long, current-carrying wire is $$B = \frac{\mu_0 I}{2 \pi r}$$; the direction is given by the right-hand rule.

The first thing to do is draw a careful diagram so you can figure out the directions of each contribution to the magnetic field. Add them (as vectors, of course) to get the total field at that point.