Hi John,
May I ask you a question about anodes and cathodes?
Mike
- Yes
Oops. Somehow this message was sent to you instead of to another user. Sorry Larry.
Mike
You are posting in a forum on the Internet, not sending a specific person a message.
Just post your question here, @skybear. The more eyes on your question, the better.
Good point, xfpd.
My question has to do with anode and cathode. In a battery, electrons flow out of the anode (-) and into the cathode (+). Anode undergoes oxidation and cathode undergoes reduction because of that. Although I'm here citing the website Geeks for Geeks (Cathode and Anode - GeeksforGeeks), I've read that definition in other places as well. It goes on to state the negative (-) end of the battery is the anode and the positive (+) end is the cathode. Okay. That makes sense.
However, other sources, such as the glossary of the Arduino project book (3rd edition, 2025) states the anode is "the positive end of a capacitor or diode" and the cathode is "the end of a capacitor or diode that typically connects to the ground."
And then there's the UMA Technology website (Anode vs. Cathode: Which Is Positive and Negative? - UMA Technology) that says in galvanic cells the cathode is considered negative and the anode is considered positive.
Now, even though the three sources are talking about different things (batteries vs. capacitors and diodes vs. galvanic cells), all three are using the same two terms (anode and cathode) but describing them in ways that seem contradictory.
I'm confused. lol.
Edited see post #9
I remember this exact point in chemistry at school some time around 1975. Someone will correct me if I have remembered incorrectly but anode and cathode are not defined by positive and negative but by direction of current flow. In the example you gave of the battery the anode is the negative pole as you describe if the battery is discharging. The anode is the pole with the electrons going in coming out. Charge the battery and the positive pole becomes the anode.
Or did you mean electron flow, which is the opposite of current flow.
Just waned to add to the confusion.
Hello Jim,
Thank you for asking. Yes, I meant electron flow.
To my way of thinking, which is perhaps not clear in my previous reply:
- Current flow: a general statement that says nothing about movement or type of charge carriers
- Conventional current flow: from positive to negative
- Electron flow: the direction electrons move, which is opposite to conventional current flow
However, I now think that what I said above is wrong, so also to add to the confusion: The anode is the pole with the electrons coming out.
If this is wrong will someone please say so!
Topic moved to general electronics.
The words "anode" and "cathode" are usually used for diodes and LEDs.
The words "+ve plate" and "-ve plate" are used for polarised capacitors.
The words "+ve post" and "-ve post" are used for Batteries.
I have heard about poles when talking on magnets -- north pole and south pole.
Electrical energy moves from the higher-potential terminal to the lower-potential terminal passing through the load. By convention, we say that current carries this energy from the source to the load. By convention, electrons flow from the lower-potential terminal to the higher-potential terminal, passing through the load along the way.
In a RC series circuit there is "conduction current" through the resistor, but it is the "displacement current" that passes through the capacitor as there is no free electrons.
Some memory helpers for Diodes:
The "A" in Anode(+) is shaped like an Arrow. The Arrow points to the negative element, Cathode(-).
There are two "current" camps. (1) "Electron" flow and (2) "Hole" flow.
The automobile and A/C hemisphere talks in Hole flow (pos to neg) of current. This camp says electrons flow in the direction of the diode arrow. This is "current" convention of the average joe. They do not know.
The Physics hemisphere talks in Electron flow (neg to pos) of current. This camp says electrons flow against the arrow, where the "A" is like a barb on a fishing hook... easy to get hooked (neg to pos), hard to get released (pos to neg). This is the real universe, but sounds "backwards" from convention. Follow this!
Cathode(-) will be connected "toward" the negative supply.
Anode(+) will be connected "toward" the positive supply.
This is where the definitions come for Electrical Engineering and Electronic Engineering:
Electrical Engineeringd deals with the flow of electrons and Electronic Engineering deals with the flow of holes.
Are you still confused, maybe now even more confused?
If you know Johns users name you can call him by using the @ sign infront of his users name like I would use @skybear to call you.
As my highschool general science teacher tried to explain, the “current” was scientifically defined and demonstrated so many years before the electron was discovered. Also the left-hand and right-hand rules for magnetism generated by current and by electron flow.
I read that the current convention was invented by Benjamin Franklin. It was what I was taught and what I believed until I started studying about volts, amps, resistance, loads, etc.
It sounds like the "definition" of anode and cathode depends on the field of electricity that you're discussing: electrical engineering, electronic engineering, physics, etc. So, like the meaning of many words, the definition of the words depend on the context of the discussion. So, if the meaning of anode and cathode does depend on the context, then I'm okay with that.
Then, and I will need some help here, which definitions of anode and cathode would suit this situation where I'm creating circuits on an Arduino?
Study vacuum tubes a bit and note that “holes” don’t cross empty space but electrons do.
When electrons move in one direction, holes move in the opposite direction, same conductor, same time. Convention says pick one, the one your parts are labelled for!
The concept of hole, as a carrier, is a mathematical entity that is present in semiconductor and NOT in mettalic conductor.