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Electricity and Magnetism

Flux Density due to Current Flowing in a Long, Straight Wire

The flux density, B, at point p is directed out of the plane of the diagram.

The magnitude of B depends on

i) the current, I
ii) the perpendicular distance, r
iii) the medium in the space around the wire.
N.B. if r is small compared with the length of the wire, then B does not depend on the length of the wire.

It can be shown that the magnitude of B is given by

where µ is the permeability of the medium

If the medium is a vacuum (or air) we write the constant as µo.

The units of µ are NA-2 or Henrys per meter (Hm-1).

 

© David Hoult 2008