Jim pointed out that the short slot is connected to the black wire which is
the "hot" wire. The long slot is connected to the white return wire. In a
modern receptacle there is a round hole which is connected to a green wire
which is the true ground. The white return wire is not a true ground and there
will probably be a small (less than 1 volt) potential difference between this
and the green wire.
Jim explained polarity one way. Another way, which I think you were asking
about, is the polarity of the "110 V" receptacle. This has to do with the long
and short slots. Most modern appliances with a two prong plug have one prong
wider than the other so that it will fit only one way into the receptacle.
I know a physicist who is a long time amateur radio operator. He lives in a
house built in the 50's which does not have polarized receptacles. Some years
back he bought a Commador computer and a small black & white TV to use as a
monitor so that he could receive teletype messages. The TV was an AC/DC model
with a polarized plug which would not fit into his older 50's receptacles
because of the wider prong on the plug. His solution was to grind the prong
down so that it would fit. The result was that he not only destroyed the TV
but also the computer.
Is this the concept of polarity you were after?
Roger
Roger A. Pruitt
Physics Department--Fort Hays State University
600 Park Street e-mail: phrp@fhsuvm.fhsu.edu
Hays, KS 67601 v-mail: 913-628-5357