Page:Electricity (1912) Kapp.djvu/189

Rh waste taking place, it is necessary to prevent currents circulating in the mass of the stator iron.

We cannot avoid an e.m.f. being generated in the iron as well as in the copper conductors, since both are side by side; but we can prevent this e.m.f. from producing a current, and this is done by interrupting its path. This means subdividing the iron into thin plates, which are insulated from each other by varnish or paper. This does not interfere with the flow of magnetism, for, as we have seen, there is always quadrature, that is, a right-angular relation between flux and the direction in which an e.m.f. is induced. Hence an insulating surface which interrupts electrical continuity is parallel to the direction of the magnetic flux, and apart from slightly reducing the available cross section for the transmission of the lines of force, does not interfere with the magnetic circuit. It may be mentioned that not only in such dynamos, but in all electrical machinery and apparatus where there is either a change of flux or a progression of flux through iron, the iron must be laminated.

It has been shown in the previous chapter that very considerable forces act on armature