# Magnitude of the resulting magnetic field

1. Aug 23, 2009

### austin007

2 long straight parallel wires separated by a distance of 20 cm carry currents of 30 A and 40 A in opposite directions. What is the magnitude of the resulting magnetic field at a point 15 cm frm the wire carrying the 30 A and 25 cm from the other wire?

How do I go about solving this problem?

2. Aug 23, 2009

### kuruman

What is the equation that gives you the magnitude of the magnetic field due to a long wire? How do you find its direction? Start from there and add the two fields because there are two wires.

** Edit **
The assumption is that the point you are considering is on a line perpendicular to the wires.

3. Aug 23, 2009

### Staff: Mentor

First find the point that they are talking about (use a bit of trig). Then find the field from each current at that point (magnitude and direction). To find the resultant field, just add the contribution from each wire. (Add them as vectors, of course.)

4. Aug 23, 2009

### austin007

It's 2 different points: one at 15 cm away from 30 A wire; the other at 25 cm away from 40 A wire.
The point does not coincides. Do I still add to get resultant or get 2 answers for 2 diff. points?

5. Aug 23, 2009

### Staff: Mentor

No, it's a single point. Otherwise the question makes no sense. (Hint: Draw circles of appropriate radius about each wire. See where they intersect.)