shanie said:
So I thought that 25 μT (12.5+12.5) would be the maximum field strength and 0 μT would be the minimum.
Assuming for the moment that 12.5 is correct, where exactly would the field strength take these values? At which points do the fields strengthen each other? Do you have an unclear visualisation of the whole of the magnetic field between and around the two wires? To get happy with these types of problems I think you need to do this visualisation (step by step).
Tricky visualisations these because they are inherently three dimensional, unlike cannon shots which you can easily visualise in two dimensions. That is you need to *clearly* see the wires going up, and the B fields circling round in the other two dimensions. Even Stephen Hawking, in "Universe in a Nutshell" says he has trouble visualising in three dimensions, adding that he can just about manage two and a half!
(Hawking, as with the God concept and too many other concepts, doesn't explain what he means by 21/2 D. Fortunately I've studied cognitive psychology so I think I know what he means. Two and half dimensions is what you get on a computer screen -- a window is two dimensional, when one overlaps another you get two a half dimensions, i.e. an impression of three dimensions without seeing the extension.)
So if you feel your mind warping and your 3D image of this situation being less than clear, don't panic! Hawking (and me) have physics degrees and we both struggle.
(Wise acres who say it's perfectly clear are either: (i) kidding themselves (ii) lucky to have a great talent and should now try it in the 11 dimensions of string theory :-)
With this problem you can't easily devolve it into two and half dimensions, so to visualise it I suggest taking a two dimensional slice. For instance, visualise the two wires. Imagine two points between the wires, the left represents the magnetic field (B) for the left wire, the right point the B field for the right wire. That is, the magnetic force is represented by a line going into the paper. You can only see its cross-section (a point).
The direction of the current and that of the resulting magnetic field are related to each other as the forward travel of a corkscrew and the direction in which it is rotated. So for the left wire imagine the point changing into a cross to indicate the field line is going into the page, and keep the right point as a point (or a small circle) to indicate the field coming out of the paper. So - left wire, cross, point, right wire, even Hawking could visualise that :-)
To get a feel for the strength of the field at various points gets a bit hairy to visualise in the "mind's eye", so get your paper and pen out and draw crosses and circles with radius proportional to the field strength at various interesting points ( I'll leave alphy to help you with calculating the field, if necessary!)