I have seen charts showing the transition from insulator to semi-conductor is at $10^{-8}~\frac{\text{S}}{\text{cm}}$ and between semi-conductor and conductor is $10^{3}~\frac{\text{S}}{\text{cm}}$. Are these switch over points arbitrary man-made conventions or is there a physical differences that sharply divides insulators, semiconductor and conductors?
I've been telling myself for example that all materials conduct electricity, it's just that some do it radically less well, up to 18 orders of magnitude less well. I'm wondering if I'm correct.
Best Answer
As you have expected, there is no sharp divide between the groups. The divide is man made.
In practice the definitions are helpful because the dynamic range between good conductors and good insulators is very large, and there are not very many situations where the middle ranges between conductor, semiconductor, and insulator prove useful.
Needless to say, those who work with high voltages (hundreds of kilovolts and above) will define the boundary between insulator and not-insulator very differently than a hobbyist tinkering with 5-10V. At higher voltages, we find the resistance of insulators starts to have more of an impact on our design, and we become more picky about how high that resistance needs to be before we call it an insulator.