1. Oct 21, 2009

### vu95112

Hell all,
The magnetic field 40 cm away from long, straight wire carrying current 2.00 A is 1 µ T. At one instance, the two conductors in a long household extension cord carry equal 2-A currents in opposite directions. The two wires are 3mm apart. Find the magnetic field 40 cm away from the middle of the straight cord, in the plane of the two wires.

2. Oct 21, 2009

### Staff: Mentor

We do not do your homework for you. What are the relevant equations, and how will you start this problem?

3. Oct 21, 2009

### vu95112

Hello,
I am sorry. I just need you help a little. Thanks
I have learn this formula
B = µ0 I / (2 п r)
Where µ0 = 4 п * 10 ^ -7, I is current , r is the radius, and п = 3.14
But, it is hard to apply on this problem

4. Oct 21, 2009

### Staff: Mentor

That is the correct equation. If you plug in the numbers in the problem statement for a single wire, do you get the 1uT B-field 40cm away from the 2A current? (Be sure to convert 40cm into meters)

If so, then you just need to superpose the two magnetic fields that you get for the two wires, and be careful about your distances. Use the right hand rule to help you figure out whether the B-fields from the two wires add or subtract out at the point 40cm away from the center of the cord (in the plane of the 2 wires).

5. Oct 21, 2009

### vu95112

Thank you very much. I got it.

6. Oct 21, 2009

Sweet.