# Terms Connected with Magnetic Materials

1. Magnetic force. It is the force exerted by one magnet on another either to attract it or repel it.
2. Unit pole strength. It is defined as the strength of that pole which when placed in vacuum at a distance of one metre from a similar and equal pole, repels it with a force of one newton.
3. Magnetic flux density (B). It is usually represented by letter B and is defined as the flux or lines of force passing per unit area through any substance through a plane at right angles to the direction of magnetic flux; it is measured in Wb/m2 (or T i.e., Tesla),
4. Magnetic field strength. It may be defined in the following two ways:
1. a.      Field strength at any point within a magnetic field is the number of lines of force passing through a unit area round the point considered and held perpendicular to the lines.
2. b.      Field strength at any point within a magnetic field is the force exerted by a unit North pole at that point.
5. Relative permeability (µr). It is the ratio of flux density (B) produced in that material to the flux density produced in vacuum by the same magnetising force (H). It is denoted by µr.
6. Absolute permeability (µ). Absolute permeability of the material is the ratio of flux density in that material to the magnetising force producing that flux density and is denoted by µ; µ = µoµr permeability of free space having a value of 4π × 10-7 H/m.
7. Magnetic potential. The magnetic potential at any point within a magneticfield is measured by the word done in carrying a unit North pole from infinity to that point against the force of magnetic field.
8. Intensity of magnetization (I). It is defined as the pole strength per unit area of the bar or magnetic moment per unit volume of the bar. It is denoted by letter I.
9. Susceptibility (K). It is denoted by the K, and is defined as the ration of intensity of magnetization (I) or magnetizing force (H). In other words K=I/H
10. Magnetomotive force. It is that force which derives or tends to drive the flux through a magnetic circuit. In short it is written as m.m.f. It is the product of number of turns (N) and current (I) in amperes in these turns i.e., m.m.f.=NI
11. Magnetic reluctance. It is that property of the material which opposes the production of magnetic flux in it.
12. Coercive force. It may be defined as the demagnetising force which is necessary to neutralise completely the magnetism in an electromagnet after the value of magnetising force becomes zero.
13. Resonance. It is defined as the magnetic flux density which still persists in magnetic material even when the magnetising force is completely removed. It is expressed in Wb / m2.
14. Retentivity. It is that property of magnetic material which is measured by its maximum value of the residual induction.  