# Parallel conductors- find magnetic field pls help!

1. Jul 21, 2009

### 9giddjl

1. The problem statement, all variables and given/known data
Consider Figure 25.14 (attached photo). In the figure, two separate wires are in close proximity. If wire A carries a current of 1.5 A and wire B carries a current of 2.5 A, calculate the value of the magnetic field strength at a point x between the two wires.

2. Relevant equations
I know that I have to find B for wire A and B for wire B and then vectorially add them. The only problem im really having is i dont know which wire has its magnetic field going into the page and which wire has its magnetic field coming out of the page. The book says wire a's magnetic field is going into the page whilst its coming out of the page for wire B. How do I know? I have used the right hand grip rule and I understand this.. im just really uncertain and abit lost...

3. The attempt at a solution

Any help will be appreciated.. thankyou kindly:)

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2. Jul 21, 2009

### Cyosis

You say you used the right hand rule and understand it, yet you don't. This is a bit confusing to me. Do you know what the magnetic field looks like for a wire, just the general 'shape'?

3. Jul 22, 2009

### 9giddjl

sorry! I thought i knew how to use the rule.. for example.. if i wrap my finger around a wire i point my thumb in the direction of the current and then my fingers represent the direction of the magnetic field? But I don't think I understand it really... could you please explain it to me?

4. Jul 22, 2009

### tigor

http://en.wikipedia.org/wiki/File:Right_hand_rule.png

if you use that rule on your problem - than magnetic field ABOVE the conductor will be FROM the page. Whereas magnetic field BELOW the conductor will be INTO the page.
Point B is BELOW conductor A and ABOVE conductor B. Therefore, Vectors of fields are opposite to one another. Naturally you will have to deduct the vectors and find the final vector.

5. Jul 22, 2009

### 9giddjl

ok that makes sense! I think I understand now...Thankyou so much!
many many thanks:)