Lesson plan
Goodness factor
The goodness factor is a metric developed by Eric Laithwaite to determine the 'goodness' of an electric motor. Using it he was able to develop efficient magnetic levitation induction motors. : G = \frac {\omega} {\mathrm{resistance} \times \mathrm{reluctance}} = \frac {\omega \mu \sigma A_\mathrm{e} A_\mathrm{m}} {l_\mathrm{e} l_\mathrm{m}} where : is the goodness factor (factors above 1 are likely to be efficient) : , are the cross sections of the electric and magnetic circuits : , are the lengths of the electric and magnetic circuits : is the permeability of the core : is the angular frequency the motor is driven at : is the conductivity of the conductor From this he showed that the most efficient motors are likely to be relatively large. However, the equation only directly relates to non-permanent magnet motors. Laithwaite showed that for a simple induction motor this gave: : G \propto \frac {\omega \mu_0 p^2} {\rho_\mathrm{r} g} where is the pole pitch arc length, is the surface resistivity of the rotor and is the air gap.
Article summary
The goodness factor is a metric developed by Eric Laithwaite to determine the 'goodness' of an electric motor. Using it he was able to develop efficient magnetic levitation induction motors. : G = \frac {\omega} {\mathrm{resistance} \times \mathrm{reluctance}} = \frac {\omega \mu \sigma A_\mathrm{e} A_\mathrm{m}} {l_\mathrm{e} l_\mathrm{m}} where : is the goodness factor (factors above 1 are likely to be efficient) : , are the cross sections of the electric and magnetic circuits : , are the lengths of the electric and magnetic circuits : is the permeability of the core : is the angular frequency the motor is driven at : is the conductivity of the conductor From this he showed that the most efficient motors are likely to be relatively large. However, the equation only directly relates to non-permanent magnet motors. Laithwaite showed that for a simple induction motor this gave: : G \propto \frac {\omega \mu_0 p^2} {\rho_\mathrm{r} g} where is the pole pitch arc length, is the surface resistivity of the rotor and is the air gap.
Key claims
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.