Notes
Always push the barrel base bearing the Hall probe along the
rule in the same direction.
1. Along the z-axis, for reasons of symmetry, the magnetic flux
density has only the axial component Bz. Fig. 3 shows how
to set up the coils, probe and rules. (The edge of the bench
can be used instead of the lower rule if required.) Measure
the relationship B (z, r = 0) when the distance between the
coils a = R and, for example, for a = R/2 and a = 2R.