Two coaxial parallel flat coils with the same radius placed a distance apart that is equal to the radius. If the same current is flowing in both coils then the value of the magnetic field strength is approximately uniform between the coils. Coils of this type are used to create fields and, in some cases, are employed to counter the effect of the earth’s magnetic field. Helmholtz coils are also used in magnetic measurement, with the coils connected to a fluxmeter. If a small magnet is placed between the coils and then removed, the integrated signal on the fluxmeter is proportional to the magnet’s magnetic moment.
An arrangement of two identical cylindrical coils mounted coaxially a distance r apart. When r just equals the radius of the coils a uniform calculable magnetic field is produced between them when the same current flows through both coils (see diagram). This arrangement was first used in the Helmholtz galvanometer but is now commonly employed when a precise uniform magnetic field is required over a substantial volume.
Helmholtz coils
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