Magnetic Flux and Flux Density

Chapter 4.4 Magnetic Flux and Flux Density

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • Magnetic Fields and Circuits 115be seen that only the toroid itself forms the magnetic circuit. Provided that it has a uniform cross-section then the fi eld contained within it will be uniform. 4.4 Magnetic Flux and Flux Density The magnetic fl ux is what causes the observable magnetic effects such as attraction, repulsion etc. The unit of magnetic fl ux is the weber (Wb). This was the name of a German scientist so it is pronounced as ‘ vayber ’ . The number of webers of fl ux per square metre of cross-section of the fi eld is defi ned as the magnetic fl ux density ( B ), which is measured in tesla (T). This sometimes causes some confusion at fi rst, since the logical unit would appear to be weber/metre 2 . Indeed, this is the way in which it is calculated: the value of fl ux must be divided by the appropriate area. Tesla was the name of another scientist, whose name is thus commemorated. On refl ection, it should not be particularly confusing, since the logical unit for electrical current would be coulomb/second; but it seems quite natural to use the term ampere. The quantity symbols for magnetic fl ux and fl ux density are and Brespectively. Hence, fl ux density is given by the equation: BAtesla(4.1)Note: references have been made to iron as a core material and as the material used for toroids etc. This does not necessarily mean that pure iron is used. It could be mild steel, cast iron, silicon iron, or ferrite etc. The term ‘ iron circuit ’ , when used in this context, is merely a simple way in which to refer to that part of the circuit that consists of a magnetic material. It is used when some parts of the circuit may be formed from non-magnetic materials.NI Fig. 4.7