Basic Laws
In the understanding of magnetism and magnetic circuits there are certain basic established laws which should be appreciated

Kirchhoffs 1st + 2nd Laws
Kirchhhoffs laws for magnetic circuits are similar to the established laws for electrical circuits

Kirchhoffs 1st Law
The total magnetic flux towards a junction is equal to the total magnetic flux away from that junction. ΣΦ = 0

Kirchhoffs 2nd Law
In any closed magnetic circuit the algebraic sum of the product of the magnetic force and the length of each part of the circuit is equal to the resultant magnetomotive force Σmmf = Σ H l

Law of Inverse Squares – Coulombs Law
The force between 2 poles of constant strength is inversely proportional to the square of the distance between them. The force between 2 magnets at a constant distance apart is proportional to the product of their pole strengths.


Terms and Definitions [A-E]

Air Gap
The distance between the magnet and the element interacting with it. In many instances the air gap is the distance between the poles of the magnet or magnetic assembly.

Ampere Turn
The product of the current, in amperes, flowing in a coil, and the number of turns of wire in that coil.

Anisotropic Material
A material that has a preferred direction of magnetization along one axis [ a magnetically oriented material ]

Area of the air gap [ Ag ]
The cross sectional area of the air gap perpendicular to the flux path, measured in sq cm.

Area of the magnet [ Am ]
The cross sectional area of the magnet perpendicular to the central flux line, measured in

B/H Curve
See Hysteresis Loop

Closed Magnetic Circuit
A circuit where the magnetic flux is conducted continually around a closed path through ferromagnetic materials. See Magnetic Circuit.

Coercive Force [ Hc ]
The demagnetizing force required to reduce the residual induction [ Br ] of the magnet to zero. Measured in Oersteds [ C.G.S ] or ampere turns [ S.I.].

Coercive Force, Intrinsic [ Hci ]
A measure of the magnet materials ability to resist demagnetization. Or stated another way it is the demagnetization force required to reduce the intrinsic induction [ Bi ] of the magnet to zero. Measured In Oersteds [ C.G.S ] or ampere turns per meter [ S.I ]

The property of a material measured by the maximum value of its coercive force.

Curie Temperature [ Tc ]
The temperature at which a magnet loses all of its magnetic properties

Demagnetisation Curve
The second quadrant portion of the Hysteresis loop [ B/H Curve ] for a magnetic material. The point on this curve are designated by [ Bd ] and [ Hd ].

Demagnetisation Force [ Hd ]
A magnetising force applied in such a direction as to reduce the remanent induction of a magnet to zero. Measured in Oersteds [ C.G.S ] or Ampere Turns [ S.I ]

Dimension Ratio [ lm / D ]
The ratio of the length of a magnet its diameter. The dimension ratio is related to the slope of the operating line of the magnet Bd / Hd.

Eddy Current
A current flow induced in a conducting material due to its relative motion in a magnetic field.

Eddy Current Loss [ Pe ]
The amount of decrease in useable magnetic energy due to eddy current generation. Part of the useable magnetic flux is consumed by its current generation, which results in a decrease in useable magnetic flux available to the rest of the magnetic circuit.

Electro Magnet
A magnet consisting of a solenoid with an iron core, which has a magnetic field existing only during the time of current following through the solenoid

Energy Product Curve
The graphic representation of the external energy produced by a magnet. The curve is obtained by plotting the product of Bd and Hd against Bd Note 1 : The peak value of the product of Bd times Hd or BHmax [ maximum values of Bd times Hd ] Corresponds to the maximum value of the external energy Note 2 : The demagnetisation curve is usually plotted to the left of the vertical axis [ negative values of Hd and the energy product curve to the right.