Important Terms in Magnetism
1) Magnetic Susceptibility (χ) — It is a measure of how much a material will magnetised in presence of an applied magnetic field.
The literal meaning of term susceptibility means how easily something can be influenced.
It is defined as the ratio of intensity of magnetisation (M) to the magnetising field intensity (H).
χ = M/H
It is a pure number. It has no units and dimensions.
2) Coercivity (Pronounced as Coecivity, r is silent) — The amount of reverse external magnetising field required to completely demagnitise a material is called coercivity of the substance.
OR
It is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without being demagnetised.
It is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without being demagnetised.
3.) Retentivity — The ability of a the magnetic field to remain inside the material even after removing the external source field is known as retentivity.
4.) Magnetic Permeability — It is the measure of the extent to which a meterial can be penetrated or permeated by a magnetic field.
It is defined as the ratio of its magnetic induction (B) to the magnetic intensity (H).
µ=B/H
*Magnetic Induction is sometimes also known as magnetic flux density.
It's SI unit is Tm/A.
5.) Relative Permeability (µr) - It is the comparative value of permeability of a substance with respect to another substance (mostly vacuum or free space in our case).
It is defined as the ratio of the permeability of the medium to the permeability of free space.
µr=µ/µ₀
µr=µ/µ₀
It is a pure number. It has no units.
6.) Curie's Law — It states that far away from saturation, the susceptibility of a paramagnetic material is inversely proportional to the absolute temperature.
7.) Importance of Hysteresis curve — The area of hysteresis curve gives heat loss.
Permeability, Susceptibility and Retentivity are greater for soft iron than for steel while Coercivity and hysteresis loss are less for soft iron than for steel.
Note :
Permeability (µ) = Magnetic flux density (B) / Magnetising Field (H)
Permeability (µ) = Magnetic flux density (B) / Magnetising Field (H)
