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I've been struggling with conversion from Gaussian to SI units for sometime, trying to figure out how derived units in CGS (current, charge etc) relate to the SI units.

But I couldn't find any reference that spoke about temperature. I've read that the only base units in CGS are the centimetre, gram and second. How does one define temperature (Kelvin) in this unit system? Or do we have to define another base unit?

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4 Answers

up vote 2 down vote accepted

When people say they are using CGS units, they mean:

  • Centimeters are the implied units of length;
  • Grams are the implied units of mass;
  • Seconds are the implied units of time;
  • Anything involving electric charge will be defined in accordance with $4\pi\epsilon_0 = 1$; and
  • All other units are the same as in SI.

Some might argue that this last point is not part of the "definition" of CGS, but it is certainly part and parcel of the working definition for astronomers, who are pretty much the sole diehard CGS fans in existence anyway.

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In both SI and CGS Kelvin is used to measure temperature, but Boltzmann's constant has different orders being expressed in corresponding units. And you can always forget about $k = 1.38 \times 10^{-16} \frac{erg}{K} $ it and measure the temperature in erg, MeV or other energetic units suitable for your problem, so you can easily compare your characteristic energies and temperature.

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There is no formal definition of the way to define temperature in this unit system. The only base units are indeed centimeter, gram and second.

If you check out the wiki page you can see that a similar system is the MKS system (meter, kilogram, seconds) and that SI is basically this MKS system with 4 additional base units: ampere, mole, candela and kelvin.

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I've read the wikipedia page, but it didn't really help with this. How do people talk about temperature in the CGS system then? –  Kitchi Mar 17 '13 at 11:08
    
I am guessing that they just use kelvin as well, but as I said: there is no formal rule because CGS only specifies the base units for length, mass and time so in principle you can use CGS in combination with any unit of temperature (kelvin, celsius, fahrenheit, rankine, whatever) –  Michiel Mar 17 '13 at 11:09
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both M.k.S. and C.G.s. unit of temp. are kelvin as well as time has a same unit that is Sec.

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