Bill Hooper wrote: >I have always found it difficult to understand how the mole >can be considered a unit of anything, photons or otherwise. >(I admit that SI does indeed define it as a unit. >But that doesn't mean that I understand it.)
I agree. The SI system also has dimensionless quantities such as refractive index. I am puzzled by how these things get in. >It is defined as the number of atoms of carbon-12 in a >sample of exactly 12 grams. I was under the impression that moles were a mere human convenience because you can't handle small quantities of molecules. You have to deal with much larger quantities such as 'the molecular weight in grams'. These are easier to deal with in the lab with simple measuring equipment. The definition in respect of carbon must be a further sophistication. I would not have thought that such a convenience was particularly deserving of the SI any more than 'light year'.
