Electric current, cathode and anode, electron flow

Jan 2020
Mumbai(Bombay), Maharashtra State, India.
While studying chemistry notes, I read about Cathode ray discharge tube, a study of which had been made by Faraday in mid 1850. When I saw definition of electric current in ' Advanced English Dictionary', it is defined as ' A flow of electricity through conductor'

Now the electricity is defined as 'A physical phenomenon associated with stationary or moving electrons and protons.' It is also defined as 'Energy made available by the flow of electric charge through a conductor.

1583313858146.pngrandom electron movements in a conductor with free electrons.

1583313991523.pngelectron flow under the action of applied electro-motive force.



Now, what is cathode?

Cathode is a negatively charged electrode(what is electrode?) that is the source of electrons entering an electrical device. it is a positively charged terminal of voltaic cell or storage batteries that suppies current.

Anode is a positively charged electrodes by which electrons leaves an electrical device.

Anode is a negatively charged terminal of voltaic cell or storage batteries that supplies current.

Now cathode is different in electric device and voltaic cell How and why?


Last edited:
Apr 2015
Now cathode is different in electric device and voltaic cell How and why?
This is a very good question where you have noted the confusion created by electrical/electronic engineers in recent times.
Largely because they don't understand Chemistry, but also because they operate two different definitions because of sign conventions.

It is good that you asked this question in a Chemistry forum because

Farady introduced the terms anode and cathode in the 1830s, along with his two laws of electrochemistry.
Here is the modern version that has been in continuous use since that time by the whole electrochemical industry, not just the battery section.
Taken from Moody's Comparative Inorganic Chemistry. I have highlighted the definitions.

Note that it is important to distinguish between the external circuit and the internal circuit.
All the charge carriers move in the opposite direction in the internal circuit from the direction they move in the external circuit.
If you think about it, this must be so for the current to move in a complete circle or circuit.

It's just that some engineers seem to have forgotten what we regard as the internal cicuit and what the external circuit and mix them up. It is important to understand which is which because directions are reversed for these two parts of a complete circuit.

So they cheerfully take a battery, write + on one terminal and draw conventional current passing out from this terminal round the 'external' circuit and back into the battery at the other one.

Yet these same engineers then take a vacuum tube, mark one terminal + and cheerfully show conventional current entering the valve at this terminal passing through the valve to the other terminal.
Strangely they want to call both these terminals marked + the anode!

The anode is the terminal of a device where electrons leave or conventional current enters.

Always. Any other use is incorrect.

But we have automobile engineers who have trouble with this as follows

Unfortunately it is probably (no disrespect meant) beyond auto techs to understand that the accumulator acts as two different devices when it is charging and when it is supplying current and that the terminals are simply the lumps of metal, but the names anode and cathode are defined by their function, not by a particular lump of metal.

So that the terminal names should therefore be reversed when charging and discharging.

So auto techs call one of the lumps of metal (terminals) the anode and (wrongly) stick to it.

For a battery being discharged, the terminal marked + is the cathode, while for the same battery being recharged, the terminal marked + is the anode.

A tricky subject indeed.