Ohm

Figure 1. A carbon resistor with the resistance of 2 MΩ, the colour code gives the resistance in Ohms.

The Ohm (Ω) is a unit of electrical resistance, useful for measuring the resistance of resistors, conductors, or even electrical insulators. The unit can be thought of as amperes/volts.

Measurements of resistance go from 0 Ω for superconductors to ~<m>10^{-6} \Omega </m> for a cm block of metal like copper or aluminum up to ~<m>10^{19} \Omega </m> for a block of sulfur. Very few physical measurements have spanned 25 orders of magnitude like this (for length that's a ratio of the thickness of a fingernail to the size of a galaxy)!

To learn more about the Ohm please see Dr. Rowlett's dictionary of units.