The weak magnetic properties of most solids can bemeasured using a Gouy balance (Figure 12.1). Inthis equipment, the sample is suspended between thepoles of an electromagnet from a sensitive balance.The vast majority of solids show only minisculemagnetic effects. Of these, most weigh slightly lesswhen the electromagnet is on than when the electromagnet is turned off. These materials, which areweakly repelled by the magnetic field, are the diamagnetic materials. The rest of the ‘non-magnetic’group weigh slightly more when the electromagnetis on than when it is off. These substances are drawnweakly into a magnetic field and are called paramagnetic materials. (Ferromagnetic materials arestrongly attracted to one or other of the pole piecesof the magnet and the technique does not give aresult.)Diamagnetic and paramagnetic substances arecharacterised by their susceptibility to the magnetic
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