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# ch15

### electromagnetic machines keywords

Term | Definition |
---|---|

Flux | What 'flows' in the magnetic field. |

Current turns | What drives the flow of flux in a magnetic circuit. |

Flux density | Magnetic field strength, how closely packed the field lines are. |

Faraday's law (in words) | Induced emf proportional to rate of change of flux. |

Flux linkage | (Flux enclosed by a coil) x (number of turns) |

Permeance | Measure of how easily flux can flow in a 'magnetic circuit'. |

B field | Magnetic field |

symbol for magnetic field strength (or flux density) | B |

symbol for flux | phi (capital = O with I through it) |

Flux density = | Flux / area (through which flux 'flows') |

Magnetically hard | Difficult to magnetise AND stays magnetic for a long time. e.g. steel |

Magnetically soft | Easy to magnetise AND loses magnetism quickly. e.g. iron |

Hysteresis | e.g. field that depends on current applied field and on previous field. |

Field lines indicate... | direction of force (on free north pole) |

domain | microscopic magnetic space within a magnetic material |

Field lines show strength ... | from their closeness together (the density of the flux) |

unit for flux | weber, Wb |

unit for field strength | tesla, T |

unit for permeance | Wb A^-1 (weber per amp turn) |

Flux (analogous to) | current (in an electric circuit) |

current turns (analogous to) | potential difference (in an electric circuit) |

permeance (analogous to) | conductance (in an electric circuit) |

emf proportional to | rate of change of flux |

emf in direction such that | it opposes change that causes it |

lines of flux tend to | shorten and straighten |

iron is laminated to... | reduce eddy currents |

permeability (analogous to) | conductivity (in an electric circuit) |

unit for permeability | Wb A^-1 m-1 (weber per amp metre) |

symbol for permeance | lambda (capital lambda = upside down V) |

symbol for permability | mu (same as for micro) |

symbol for current turns | NI |

unit for current turns | A (amp turns) |