The anode is known as the electrode responsible for the oxidation reaction of the elements. A big mistake that was developed is thinking that its polarity is eternally positive. Most of the time this concept is wrong since depending on the device used the polarity can vary and to this is added the way it works taking into account the flow and direction of the electric current. Putting things a little clearer, the anode is positive if it absorbs energy and negative when it supplies it.


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  • 1 History
  • 2 Thermoionic valves
  • 3 special anodes
  • 4 Source


Faraday was the first person to use the term “anode” in one of his books called “Experimental Explorations on Electricity .” It gave him an access meaning, or ascending path, but only by pointing to an electrolyte in the electrochemical cells. In his principle he asserts that it is positive charges that move and maintain this element, but, as we have previously explained, this is not the case in all cases, and in most cases the charge is negative.

It is true, apparently and at first glance, it is logical to define which is the direction of the electric current , appreciating it as a direction of movement of the free charges, but, if the conductor is not metallic, positive charges arise that move on the external conductor.

This implies that we have negative and positive charges moving in opposite directions and therefore the definition of the direction of current is adopted in a convention, such as the path of the positive charges of the cations to the negative charges of the anodes (anode – cathode ).

On the other hand, if the case infers a low power , the anodes must be of good size to absorb the impact of all the electrons that are subjected to a voltage difference between the aforementioned, anodes and cathodes. The impact causes the transfer of energy and this dissipates in the form of heat .

There are also so-called special anodes, these are anodes that are present for example in X-ray tubes . These X-rays are generated at the moment when the anode is subjected to a large energy charge. The electrons are then irradiated in the form of rays and heat the anode tremendously. For this reason the anode is large, and is provided with sinks that work with air or water to cool it

Thermoionic valves

The anode of thermoionic valves receives most of the electrons emitted by the cathode. When it comes to amplifier tubes ( triode , tetrode or pentode ) and especially if they are valves of power , this electrode is responsible for the heat generated in the tube, which should dissipate. There are two strategies for this: In the case of high power, the anode is thermally coupled to a heatsink outside the valve that is cooled by circulating air , steam , oil, etc. In case of lower power, the anodes are large, with a large surface to the outside, so that they dissipate by radiation. The origin of this heat is in the energy that the electrons acquire when subjected to the difference in voltage between the cathode and the anode. On impacting the anode, they give up their energy, which dissipates as heat.

Special anodes

Certain valves feature special anodes, such as the X-ray tube (Röntgen tube). X-rays are generated by striking high-energy electrons against the anode atoms, usually Wolfram or Molybdenum. The energy of these electrons, in addition to being radiated in the form of X-rays, heats the anode enormously, making it large, provided with dissipators, by air or water, and is usually rotary, with a motor that moves it to distribute the incidence of electrons over a large area. In the case of cathode ray tubes , the anode surrounds the screen and is connected to it by a thin layer of aluminumdeposited on the tube. In the case of magnetrons, the anode usually takes the form of resonant cavities at the operating frequency .


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