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ch15

electromagnetic machines keywords

TermDefinition
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)
Created by: allydavies