How to find an expected value for magnetic field strength?

[jstrahan]

Homework Statement

For my yr12 phyics assignment, I am struggling to find an expected value for magnetic field strength at a specific distance.

Relevant Equations

B=2*10^-7 (I/r) (where I is current and r is distance. B is magnetic field strength in Tesla)
B is proportional to 1/r^2 (this is the relationship that was expected, however the relationship was found to be a power relationship).

Our class modified an experiment to measure the magnetic field strength in mT between 5cm and 30cm, and I have plotted data and found that the relationship resembles a power relationship (using a log vs log graph). In order to find the percentage uncertainty for the whole experiment I need the expected value for the gradient of that log vs log graph, but I am struggling to find a formula that will work with the magnetic field strength and distance variables. Does anyone know of a formula that could be beneficial to me? I've attached some formulas below that are available in our curriculum, however, they do not seem to match the exact situation we have set up (they involve current, etc). Any amount of help would be greatly appreciated!

 

[Charles Link]

We need to have a better description of the apparatus that was creating the magnetic field. It is likely there is a formula available, but it is necessary to know the geometry of the apparatus, as well as any electrical currents that may be present.