Assertion: magnetic field | /r/AtLocation | the field poles
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text: We saw that if enough residual magnetic flux remained in the field poles after the machine had been switched off, the e.m.f. produced when the shaft was rotated could begin to supply current to the field winding, thereby increasing the flux, further raising the e.m.f. and initiating a positive feedback (or bootstrap) process which was ultimately stabilised by the saturation characteristic of the iron in the magnetic circuit.