An important fact about
anodes and
cathodes is that chemical processes will occur when they are submerged. For example,
electrolysis occurs when
electrodes are dropped into salty water. (The water has to be salty so that it will
conduct electricity.) The chemical process created causes
oxygen to be released from one electrode, and
hydrogen from the other.
The process at the anode is called oxidation, and the process that occurs at the cathode is reduction. A good nmemonic for the whole thing is the sentence, "An ox and a red cat".
This finds practical application in many areas, and one known to most people (whether they know it or not) involves the "zincs" on a boat. They are pieces of sacrifical metal performing as the anode in cathodic protection, creating a beneifical electrical field to keep the propellers from corroding away.