Letter O

OHM -- A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm. It is given the symbol 'R' in calculations and can be found by dividing VOLTS with AMPERES.

OHM's LAW - Named for Georg Simon Ohm, a law of physics that says at constant temperature, the current flowing through a metalic conductor is propotional to the potential difference between the ends.

OZONE - A kind of oxygen that has three atoms per molecule instead of the usual two. Ozone is a poisonous gas, but the ozone layer in the upper atmosphere shields life on earth from deadly ultraviolet radiation from space. The molecule contains three oxygen atoms (O3).