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ElectrodeAn electrode is a conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron (meaning amber, whence the word electricity is derived) and hodos, a way [1].
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An electrode in an electrochemical cell is referred to as either an anode or a cathode, words that were also coined by Faraday. The anode is defined as the electrode at which oxidation occurs, and the cathode is defined as the electrode at which reduction occurs. Each electrode may become either the anode or the cathode depending on the type of reaction occurring in the cell.
A primary cell[?] is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. It can be discharged but not recharged. The anode is always the negative (-) electrode and the cathode always the positive (+).
A secondary cell, for example a rechargeable battery, is one in which the reaction is reversible. When the cell is being charged, the anode becomes the positive (+) electrode and the cathode the negative (-). This is also the case in an electrolytic cell[?]. When the cell is being discharged, it behaves like a primary or voltaic[?] cell, with the anode as the negative electrode and the cathode as the positive.
In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors[?]) the anode is the positive (+) electrode and the cathode the negative (-).
See also:
Fifty or sixty different kinds have been discovered,
bone, not a fragment, of any one of the animals.html">animals which left these
which have been met with in all these deposits, from the time of
carefully hunted over--is a fragmentary skeleton of one of the
animals? You see we are not dealing with little creatures, but
remains must have been left somewhere. The probability is, that
which there was nothing left except casts of the bones.html">bones.html">bones, the
percolating water. It was a chance, in this case, that the
to allow the bones to be afterward dissolved out, leaving
been other than what it was, the bones would have been
into one mass, and not the slightest indication that the animal
the caution which should be used in drawing the conclusion, from
plants.html">plants did not exist.html">exist at the time it was formed. I believe that,
one hand, and a just estimation of the importance of the
difficulty is removed from the kind of evidence to which I have
cases are examples of what I have designated negative or
advance the hypothesis of evolution.html">evolution.html">evolution.html">evolution, but they are not to be
reasons which I will point out to you by and by, are not to be
are such as must exist if evolution be true.html">true, and which therefore
doctrine of evolution be true, it follows, that, however diverse
all, at one time or other, have been connected by gradational
down to the lowest speck of protoplasmic matter in which life
of the series to the other, either exists or has existed.
evolution. But when we look upon living Nature as it is, we find
plants fall into groups, the different members of which.
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