Due to the symmetry, on the chosen integration contours, the induction field produced by / current that flows through the reel is always tangential at contour and has constant amplitude. The result is:
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(1) |
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(2) |
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(3) |
where m0 represents the magnetic permeability of the vacuum and of the air, and m represents the magnetic permeability of the material from which the annular core is made.
It is ascertained that in any point outside the torus, the field is null. The entire flux induced by the current, circulates, therefore, within this volume, similar to an electrical circuit in which the power only flows through conductors. By analogy, we can define torus as being a magnetic circuit.
1 actually,for any contour situated in a plan which does intersect the reel.