I hope this clears this up some: )
How to Define Anode and Cathode
* Definition <http://www.av8n.com/physics/anode-cathode.htm#i-def>:
The anode of a device is the terminal where current flows in. The
cathode of a device is the terminal where current flows out.
* Our definition applies easily and correctly to every situation I
can think of (with one execrable exception, as discussed below
<http://www.av8n.com/physics/anode-cathode.htm#i-zener>). Good
examples you might have heard of include cathode-ray tubes, the
cathode/grid/plate in an amplifier tube, the rotating anode in an
Xray tube, common-anode LED arrays, and the sacrificial anode on a
boat.
* Ours is the original, time-honored definition. It is consistent
with the Greek roots ανα- and κατα-. There is no other sensible
definition. I’ve seen several attempts at definitions, but unless
they were equivalent to our definition
<http://www.av8n.com/physics/anode-cathode.htm#i-def>, they were
grotesquely overcomplicated, wrong, or both.
* For the vast majority of people, there is no point in memorizing
the meaning of anode and cathode. The terms just aren’t very
useful, unless you get a job in an electrochemistry laboratory or
some comparably narrow specialty. If some day you do need to know
the meanings, you can look them up that morning and forget them
again that evening.
* Note that when we say current-in, we mean current flowing into the
device from the external circuit. Similarly when we say
current-out, we mean current flowing out of the device toward the
external circuit. We are treating the device as a black box, and
we are not talking about whatever currents flow within the device.
This black-box terminology is standard in all branches of
engineering and science, unless the context clearly requires
otherwise.
* To avoid misconceptions, remember that the anode/cathode
distinction is based on current, not voltage. Anode/cathode is not
the same as positive/negative or vice versa. Illustrative example:
for a battery being discharged, the positive terminal is the
cathode, while for the same battery being recharged, the positive
terminal is the anode.
Bottom line: Anode/cathode means current-in/current out.
Dan Nave wrote:
Everything that I've ever seen defines the anode as the positive
electrode...
Dan
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