Teaching Minds-On Experiments on Electromagnetism in Secondary Schools

Permanent magnets
The deviation of a compass needle brought close to a magnet

We place a sheet of what such that its smaller end points in the same direction as a compass needle placed on top of it. We place a cylindrical magnet at a fair distance from the needle of the compass, so that it remains perpendicular to the axis of the magnet. We bring the compass closer to the magnet. We record the direction of the compass needle at different distances from the magnet: it forms an angle which becomes more acute as it approaches the magnet. The projection of this direction along the direction of approach represents the component of the magnetic field caused by the magnet (Bm), with respect to the fixed component of the Earth’s magnetic field (Bt). If we trace a parallel line along the direction of approach, we measure Bm in arbitrary units, measuring the length of the projection upon this from the direction of the needle. Bm grows rapidly as the distance (d) diminishes between the compass and the magnet. We find that Bm*d3= const. This type of dependence we call “dipole” one: clearly, the magnet used has two poles (north and south), so it is a di-pole.
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