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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) |