Cathodes/Anodes in Chemistry and Physics

  • Thread starter quanticism
  • Start date
29
3
Hi,

I'm confused at why cathodes are the positive terminal in chemistry but appear to be the negative terminal in physics. I hope someone can clear this up for me.

Definitions:
Anode: An anode is an electrode through which conventional current flows into a polarized electrical device.
Cathode: A cathode is an electrode through which conventional current flows out of a polarized electrical device

Galvanic Cell
Galvanic_cell_with_no_cation_flow.png


Vacuum Tube
cathode-rays-formation.jpe


Going by the definition above, I agree with the galvanic cell "cathode/anode" labels.

However, looking at the vacuum tube, the electrons traveling to the right through the partial vacuum and entering the anode, ie conventional current is leaving the anode which seems to contradict the provided definition.
 

AlephZero

Science Advisor
Homework Helper
6,953
291
The definitions describe what happens outside the device.

Inside the CRT, electrons travel from the cathode to the anode.

Outside the CRT, to complete the circuit, electrons travel from the anode to the cathode.

So outside the CRT, conventional current travels from the cathode to the anode.

So conventional current flows from outside the CRT into the anode.
 
29
3
Thank you very much! I finally see the light now :)
 
There is a difference between conventional current (taken as flowing from positive to negative) and electron current. This link will explain it and the history of the convention. http://web.engr.oregonstate.edu/~traylor/ece112/lectures/elect_flow_vs_conv_I.pdf [Broken]
 
Last edited by a moderator:
139
7
The electrons are reppeled from Cathode and attracted to Anode.
The electrons in galvanic cell can not move trough the Porous disk, and they move trough the outside circuit.
 
Last edited:

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