1. Feb 22, 2010

### Kawakaze

Hi everyone, long time lurker, first time poster. Can someone please clear this up for me? Two wires running parallel to each other. I think its just an algebraic addition of the usual

B(r)=u_0i/2pir

but instead of r, we are using D and d

aslso i apologise for my formulae, if someone could point me to the tex thread ill redo them

1. The problem statement, all variables and given/known data

By summing the magnetic field due to currents of magnitude i flowing in both the wires in the senses you found in part (c), show that, on the line joining the two wires, the magnetic field strength is given by =

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2. Relevant equations

B(r)=u_0i/2pir

3. The attempt at a solution

B=(u_0i/2piD)+(u_0i/2pid)

which i get to be

B=(u_0i)/pi(D^2-d^2)

the question says it should be

B=(u_0iD)/pi(D^2-d^2)

Where is that extra D on the numerator from?

Thanks

2. Feb 22, 2010

### kuruman

We can't help you unless you post the entire problem as stated. What are the "senses you found in part (c)"? What do parts (a) and (b) ask? Guessing at what might be asked does not help us help you.

3. Feb 22, 2010

### Kawakaze

Parts a and b have no bearing on the question. This is just an algebra question. I found out where i went wrong. Just bad practice! =/