for a magnetic circuit constructed of different materials or non-homogeneous materials or both, the permeability of a hypothetical homogeneous material which, when used to construct a circuit of identical dimensions, would provide the same reluctance
NOTE 1 – Where the different materials are in series along the magnetic path and the permeability can be assumed constant over any cross-section, the following equation is applicable:
where l is the length, measured along the magnetic path, of each part of the core of uniform cross-section A and homogeneous permeability µr.
NOTE 2 – The effective permeability is used particularly in relation to cores having (air) gaps and it is usually restricted to cases where the leakage flux is relatively small.
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