# #modphys 18/180: Magnetic Field

I’ve been using the Electricity & Magnetism modeling materials with my grade 12 physics class, pulling out segments and re-arranging models to fit our fields-based approach. Today I introduced the magnetic field using the paradigm lab(s).

One conceptual difficulty we hit (not for the first time!) is the conceptual hurdle involved in using  quantity that is proportional to the quantity we are trying to measure. Here, we measured the angle between north and the direction a compass points near a current-carrying wire. Then, through a trigonometric argument, we used the tangent of that angle as a stand-in for the strength of the magnetic field caused by the wire at that point. Thus, our linearized graph eventually showed that tan(angle) is directly proportional to the inverse of the distance.

I’m not sure there is a better way to do this paradigm lab, but we did play around a bit with ways to visualize the sum-of-two-magnetic-field-force-vectors.

We found a bag of tiny compasses, which seemed to work pretty well (although they sometimes needed a tap to remind them of their profession!). Here, they are aligned with no current flowing through the wire. I accidentally deleted my photo of the compasses with current flowing — I’ll try to recreate it next week.

I think next week we’ll work with the apparatus again, to try to eek out F=qvB (although, more usefully but I think less conceptually clear, we’ll probably have to aim for F=LiB).