A Faraday balance is a device used to measure

magnetic susceptibility In electromagnetism, the magnetic susceptibility (; denoted , chi) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the applied magnet ...

, a property of matter is related to the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

experienced by a substance in a

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

. Various practical devices are available for the measurement of susceptibility, with differences in the shape of the field and the way the force is measured. In the Faraday balance, the magnetic field is

homogeneous Homogeneity and heterogeneity are concepts relating to the uniformity of a substance, process or image. A homogeneous feature is uniform in composition or character (i.e., color, shape, size, weight, height, distribution, texture, language, i ...

. The pole pieces of the

magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

are shaped so that there is a region in which the product of the field strength and the field gradient in the ''z'' direction is constant; the sample to be measured is placed in this region. The force in this case is independent of the packing of the sample and depends only on the total

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

of the material present. The method is sensitive and highly reproducible, and can be applied to single crystals. The force is measured as a

weight In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition. Some sta ...

change using a torsion balance. An alternative method for measuring magnetic susceptibility is the Gouy balance. In this technique there is an inhomogeneous magnetic field in the central region between two (flat) poles of a magnet, either a permanent magnet or an

electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...

. The sample must be in powder form and is placed in a cylindrical tube, which is then suspended in such a way that one end lies in the centre of the field and the other is effectively outside the magnetic field. However, errors caused by inefficient packing in the sample tube are difficult to eliminate.

References

Magnetic devices {{electromagnetism-stub