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In my last blog entry I talked about the CGS unit system, an unit system based upon centimeters, seconds, and grams that was forced into obsolescence with the near universal adoption of the SI system. Although there is no question that the universal adoption of a single clearly defined unit system is beneficial and economical, there are sacrifices. Some unit systems are simply better suited for certain topics than others. Today I will cover the CGS units of Electrodynamics.
SI treats current (Ampere) as the fundamental quantity and charge as simply a quantity derived from current (rather than vice-versa). The CGS unit system uses charge (esu) as its fundamental unit. In CGS, the unit of charge, esu, is defined as the amount of charge, seperated by 1 cm, that produces 1 dyn of force. That makes esu = dyn·cm2 The beauty of the esu unit is that this definition automaticaly builds 1/4πε0 into its units, resulting in equations that look like:
F= (q1q2)/r2
since
F= (dyn·cm2)x1/cm2 = dyn
instead of F=(1/4πε0)(q1q2)/r2 as in the SI system
Many of the frequently used equations found in electrodynamics are thus simplified in this way. For this reason, there has been a reluctance by those who grew up with CGS to switch to SI. Still, despite the convience, we're all better off with a single unit system.
Electrodynamics
Charge - electrostatic unit of charge (esu) - Franklin (Fr) - Statcoulomb (statC)
Electric Current - esu/s
Electric Potential - statvolt (statV) - erg/esu
Electric Field - statV/cm - dyn/esu
Magnetic Field Intensity - Oersted (Oe) - dyn/esu
Magnetic Flux Density (aka Magnetic Induction) - Gauss (G)
Magnetic Flux - Maxwell (M) - G·cm2
Magnetic Dipole Moment - electromagnetic unit (emu) - G·cm3
That's all for now. Special thanks to the following websites:
http://web.mit.edu/8.06/www/handouts/units.pdf
http://www.unc.edu/~rowlett/units/cgsmks.html
http://en.wikipedia.org/wiki/Cgs
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