Laws of Magnetic Force
Coulomb was once the first to determine experimentally the quantitative expression for the magnetic drive between two isolated point poles.
It is usually famous here that, in view of the truth that magnetic poles always exist in pairs, it is unimaginable, in follow, to get an isolated pole.
The concept of an isolated pole is purely theoretical. Nonetheless, poles of a skinny however lengthy magnet is also assumed to be factor poles for all practical functions. By means of utilising a torsion stability, he located that the force between two magnetic poles placed in a medium is
(i) directly proportional to their pole strengths.
(ii) inversely proportional to the square of the distance between them.
(iii) inversely proportional to the absolute permeability of the surrounding medium.
Magnetic Field Strength (H)
Magnetic field strength at any point within a magnetic field is numerically equally to the force experienced by a N-pole of one weber placed at that point.
Hence, unit of H is N/Wb. Suppose, it is required to find the field intensity at a point A distant r metres from a pole of m webers. Imagine a similar pole of one weber placed at point A. The force experienced by this pole is F = 2 0 1 4 m r × Ï€Î¼ N ∴ H = 3 04 m rπμ N/Wb (or A/m)*** or oersted. Also, if a pole of m Wb is placed in a uniform field of strength H N/Wb, then force experienced by the pole is = mH newtons. It should be noted that field strength is a vector quantity having both magnitude and direction.
It would be helpful to remember that following terms are sometimes interchangeably used with field intensity : Magnetising force, strength of field, magnetic intensity and intensity of magnetic field.
Weber and Ewing’s Molecular Theory
This theory was once first evolved with the aid of Weber in 1852 and was once, later on, extra developed by means of Ewing in 1890.
The basic assumption of this conception is that molecules of all components are inherently magnets in themselves, every having a N and S pole.
In an unmagnetised state, it’s supposed that these small molecular magnets lie in all different types of haphazard manner forming roughly closed loops.
According to the legal guidelines of enchantment and repulsion, these closed magnetic circuits are satisfied internally, thus there’s no resultant outside magnetism exhibited by means of the iron bar.
But when such an iron bar is positioned in a magnetic area or underneath the impact of a magnetising drive, then these molecular magnets start turning circular their axes and orientate themselves roughly along straight strains parallel to the path of the magnetising force.
This linear arrangement of the molecular magnets results in N polarity at one finish of the bar and S polarity at the other.
As the small magnets flip more close to within the direction of the magnetising drive, it requires more and more of this force to provide a given turning moment, for that reason accounting for the magnetic saturation.
On this theory, the hysteresis loss is supposed to be due to molecular friction of those turning magnets.
Because of the confined talents of molecular structure available on the time of Weber, it used to be now not possible to explain firstly, as to why the molecules themselves are magnets and secondly, why it’s inconceivable to magnetise special components like timber etc.
The primary objection was defined through Ampere who maintained that orbital motion of the electrons round the atom of a molecule constituted a flow of current which, as a result of its associated magnetic influence, made the molecule a magnet.
Afterward, it grew to become difficult to explain the phenomenon of diamagnetism (shown via substances like water, quartz, silver and copper and many others).
Erratic behaviour of ferromagnetic (intensely magnetisable) materials like iron, metal, cobalt, nickel and some of their alloys and so forth. And the paramagnetic (weakly magnetisable) substances like oxygen and aluminium and so forth.
Moreover, it was once asked : if molecules of all supplies are magnets, then why does not wood or air etc. Become magnetised ? All this has been explained satisfactorily by way of the atom-domain idea which has outdated the molecular idea.
It is beyond the scope of this publication to enter the small print of this concept. The reader is instructed to refer to some common publication on magnetism.
However, it’s going to simply be stated that this theory takes into account not best the planetary movement of an electron however its rotation about its possess axis as good. This latter rotation is referred to as ‘electron spin’.
The gyroscopic behaviour of an electron gives upward push to a magnetic moment which could also be either optimistic or negative. A substance is ferromagnetic or diamagnetic for this reason as there’s an far more than unbalanced constructive spins or bad spins.
Supplies like wooden or air are non-magnetisable considering that of their case, the optimistic and poor electron spins are equal, therefore they cancel each other out.
Curie Point
As a magnetic fabric is heated, its molecules vibrate more violently. As a final result, man or woman molecular magnets get out of alignment because the temperature is improved, thereby decreasing the magnetic force of the magnetised substance. Approximate cut down of magnetic force with upward thrust in temperature.
Surely, it is possible to partly or even totally smash the magnetic homes of a material by way of heating.
The temperature at which the vibrations of the molecular magnets end up so random and out of alignment as to curb the magnetic force to zero is called Curie point.
More accurately, it is that crucial temperature above which ferromagnetic material becomes paramagnetic.
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