Editing Electric motor (section)

===Goodness factor===
{{main|Goodness factor}}
[[Eric Laithwaite]]<ref name="Laithwaite2">{{cite journal|last=Laithwaite|first=E.R.|date=February 1975|title=Linear electric machines – A personal view|journal=Proceedings of the IEEE|volume=63|issue=2|pages=250–90|bibcode=1975IEEEP..63..250L|doi=10.1109/PROC.1975.9734|s2cid=20400221}}</ref> proposed a metric to determine the 'goodness' of an electric motor:<ref name="Patterson (2003)2">{{cite conference|last=Patterson|first=D.J.|author2=Brice, C.W.|author3=Dougal, R.A.|author4=Kovuri, D.|date=1–4 June 2003|title=The "Goodness" of Small Contemporary Permanent Magnet Electric Machines|url=http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf|publisher=IEEE|volume=2|pages=1195–200|doi=10.1109/IEMDC.2003.1210392|isbn=0-7803-7817-2 |archive-url=https://web.archive.org/web/20100613193529/http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf|archive-date=13 June 2010|book-title=Electric Machines and Drives Conference, 2003. IEMDC'03|url-status=live}}</ref>
:<math>G = \frac {\omega} {\text{resistance} \times \text{reluctance}} = \frac {\omega \mu \sigma A_\text{m} A_\text{e}} {l_\text{m} l_\text{e}}</math>

Where:

: <math>G</math> is the goodness factor (factors above 1 are likely to be efficient)
: <math>A_\text{m}, A_\text{e}</math> are the cross sectional areas of the magnetic and electric circuit
: <math>l_\text{m}, l_\text{e}</math> are the lengths of the magnetic and electric circuits
: <math>\mu</math> is the permeability of the core
: <math>\omega</math> is the angular frequency the motor is driven at

From this, he showed that the most efficient motors are likely to have relatively large magnetic poles. However, the equation only directly relates to non PM motors.