Electronics Principles V11

Clive W. Humphris

MAGNETISM: Attraction and Repulsion.  


By placing two bar magnets (magnetic iron) end to end they either attract or repel one another.

A bar magnet is referred to as a permanent magnet because it retains its magnetic properties. Around each magnet there exists a magnetic flux which when brought into the range of a similar field will cause the two bodies to be either attracted or repelled. When positioned to attract, the result is that of one long magnet where the path of the flux is directed through both magnets.

The strength of a magnet (flux, unit Weber) may be expressed by the number of lines of force leaving the N pole and entering the S. Flux density varies around the magnet but is concentrated at the poles and is the number of lines of force passing through an area of 1sq cm. Here the unit of measurement is the tesla, symbol (T) where one tesla is a density of one Weber of magnetic flux per square metre.

The physical size of a magnet is not related to its magnetic strength, this depends upon the flux density.


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