Cathodes/Anodes in Chemistry and Physics

  1. 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
    [​IMG]

    Vacuum Tube
    [​IMG]

    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.
     
    davidbenari likes this.
  2. jcsd
  3. AlephZero

    AlephZero 7,298
    Science Advisor
    Homework Helper

    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.
     
    davidbenari likes this.
  4. Thank you very much! I finally see the light now :)
     
  5. 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: Dec 6, 2013
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