# Homework Help: B field btwn two current carrying wires

1. Apr 18, 2004

### sonya

I just had a quick thing i wanted to clarify...

The question was:
If u have two horizontal parallel current carrying wires 196 cm apart, with the bottom wire carrying a current of 2.2 A to the west and the top 1.1 A to the west, what is the magnetic field at the point P? Point P being the midpoint between the 2 wires.

What I thot you would do is just find the 2 separate B-fields due to each wire and then add them. However, the answer in the book says that it is just the field due to bottom wire. I was wondering why this is and how come otherwise we add the fields, or subtract depending on the current direction.

2. Apr 18, 2004

### Staff: Mentor

Yes, you add the separate B-fields.

The B-field is a vector. (Use the right hand rule to find the direction of the field.) The field from the top wire (carrying 1.1 A) is directed opposite to the field from the bottom wire (carrying 2.2 A). (Assuming one wire is directly beneath the other.)

I don't see how the book's answer can be right.