A current dipole may be idealized as a source and sink with equal magnitude, separated by an infinitesimal distance d. This may be written formally as
where r+ (r_) is the source (sink) location, and d = r_ — r+ is the directed distance from sink to source.4 Inserting (4.6) into (4.5) leads to an intuitive expression for the dipole moment:
where I0 is the magnitude of the current, and d is the directed distance from source to sink.
4 Technically, the limit d ^ 0 refers to the dual limit: d ^ 0 and I0 that the product p = I0d remains constant and finite.
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