Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 6 down vote favorite
1

When I was younger I learned in Chemistry class that Anions were negatively charged and Cations were positively charged (Fun fact: I memorized this because anion sounds like onion which makes you cry and is therefore negative; while cation has cat in it and cats are cute, so it's positive :P).

Now that I've started getting into electronics, I've learned that the Anode is the positive lead while the Cathode is the negative one. It seems odd to me that they're reversed; can someone explain why this is?

share|improve this question
1  
Another possible mnemonic: A "cation" is positive because it has the letter "t" in it and it looks like the positive symbol. :-) – In silico Apr 15 '12 at 22:35
1  
For diodes the mnemonic I use is AAA - Anode Acceptor Arrow: The anode is comprised of acceptors (i.e. holes are the conductors) and on the symbol it is the arrow. The complementary mnemonic isn't as nice. CDB - Cathode Donor Bar, The cathode is comprised of Donors (i.e. electron conduction) and the symbol has a bar on that end. – rawbrawb Mar 5 at 17:05

5 Answers

up vote 5 down vote

From Wiki:

Faraday also introduced the words anion for a negatively charged ion, and cation for a positively charged one. In Faraday's nomenclature, cations were named because they were attracted to the cathode in a galvanic device and anions were named due to their attraction to the anode.

In the diode, and specifically in the so-called depletion region, there is diffusion of carriers (electrons and holes) from one region to the other. Since the Anode is positively doped, it will attract electrons from the cathode, and this will cause the formation of Anions in its side of the depletion region.

share|improve this answer
The names cathode and anode were around before semiconductor diodes. The name diode was extended to semiconductor devices that had the same one-way current property of the existing diodes of the day, which were mostly vacuum tubes. The "di" in diode refers to 2. A "diode" was a 2-element tube, as apposed to a triode, pentode, and others. – Olin Lathrop Mar 5 at 16:55
up vote 2 down vote

IIRC anions are the ions that are attracted to the anode in an electrolytic cell. Opposite charges attract, hence the charge of an anion is opposite of that of an anode.

An electrolytic cell (not to be confused with a galvanic cell!) decomposes chemical compounds by means of electrical energy, in a process called electrolysis [ http://en.wikipedia.org/wiki/Electrolytic_cell ]

share|improve this answer
+1. That's what I recall from my chemistry classes, too. (Also, I recall my favorite chemistry teacher saying: "If you know what you're doing, you may do anything." True for electronics engineering as well!) – zebonaut Apr 15 '12 at 20:44
-1 an anode does not have a specifically signed charge. This will get you confused when looking at batteries. – noah1989 Apr 16 '12 at 12:10
added 'in an electrolytic cell' – Wouter van Ooijen Apr 16 '12 at 13:45
still, in a battery the charge of an anion has the same sign as the anode. your explanation refers to anodes always being positively charged, which is not correct. – noah1989 Apr 16 '12 at 13:58
@noah1989 it's true, but in this case electrons are attracted by the anode because of carrier diffusion, so the principle somehow holds – clabacchio♦ Apr 16 '12 at 14:10
show 5 more comments
up vote 1 down vote

The anode is not always the positive lead.

It is the electrode through which electric current flows into a polarized electrical device. For a discharging battery, this is the negative lead.

This is how I connected anode/anion and cathode/cation during chemistry class when we were discussing batteries. I was confused when I learned that for other components, such as an LED, the kathode is negative, and the anode is positive. Until I learned that it's not about polarity but about the direction of current flow (anode = in, cathode = out), and the naming of ions is based on how they move in a discharging battery, probably because that's what chemists often deal with.

share|improve this answer
up vote 0 down vote

The anode have negative chare because it don't do workers without the cathode , so cathode have positive charge due to its efficiency of giving - es

share|improve this answer
up vote 0 down vote

As the anode have negative charge because it takes the m - es from cathode i-e positive charge because influence of the nucleus to the around revolving es is more as well as less in rare cases so it hold the es permanently in this way the consumer is cation and saver is anion sion work done is taken by cation therefore it is positive and opposite to this is for cation because it alone do nothing

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.