ELECTROMAGNETISM
A permanent magnet is a piece of ferromagnetic material (such as iron,nickel or cobalt) which has properties of attracting other pieces of these materials. A permanent magnet will position itself in a north and south direction when freely suspended. The north-seeking end of the magnet is called the north pole, N, and the south-seeking end the south pole, S. The area around a magnet is called the magnetic field and it is in this area produced by the magnet can be detected. A magnetic field cannot be seen, felt, smelt or heard and there fore is difficult to represent. that the magnetic field could be represented pictorially, by imagining the field to consist of lines of magnetic flux,which enables investigation of the distribution and density of the field to be carried out.
If a compass is placed in the magnetic field in various positions, the direction of the lines of flux may be determined by noting the direction of the compass pointer. The direction of a magnetic field at any point is taken as that in which the north-seeking pole of a compass needle points when suspended in the field. The direction of a line of flux is from the north pole to the south pole on the outside of the magnet and is then assumed to continue through the magnet back to the point at which it emerged at the north pole. Thus such lines of flux always form complete closed loops or paths, they never intersect and always have a definite direction. The laws of magnetic attraction and repulsion can be demonstrated by using two bar magnets. . Lines of flux are imagined to contract and the magnets try to pull together. The magnetic field is strongest in between the two magnets, shown by the lines of flux being close together. with similar poles adjacent (i.e. two north poles), repulsion occurs, i.e. the two north poles try to push each other apart, since magnetic flux lines running side by side in the same direction repel.
Magnetic flux and flux density
Magnetic flux is the amount of magnetic field (or the number of lines of force) produced by a magnetic source.The symbol for magnetic fluxis (Greek letter ‘phi’). The unit of magnetic flux is the weber, Wb. Magnetic flux density is the amount of flux passing through a defined area that is perpendicular to the direction of the flux:
The symbol for magnetic flux density is B. The unit of magnetic flux density is the tesla, T, where 1 T=1Wb/m2. Hence
