Anode and cathode - what is it and how to correctly determine it?

The anode and cathode of the power supply must be known to those who are engaged in practical electronics. What do they call it? Why so? There will be an in-depth consideration of the topic from the point of view not only of radio-amateurs, but also of chemistry. The most popular explanation is as follows: the anode is a positive electrode, and the cathode is negative. Alas, this is not always true and incomplete. To be able to determine the anode and the cathode, it is necessary to have a theoretical basis and to know that yes how. Let's look at this within the framework of the article.

Anode

Let's turn to GOST 15596-82, which deals with chemical sources of current. We are interested in the information on the third page. According to GOST, the negative electrode of a chemical current source is precisely the anode. Here so yes! And why exactly? The fact is that it is through him that the electric current enters from the external circuit into the source itself. As you can see, not everything is as easy as it seems at first glance. You can advise carefully consider the pictures presented in the article, if the content seems too complicated - they will help to understand what the author wants to convey to you.

Cathode

We address all to the same GOST 15596-82. The positive electrode of the chemical source of current is the one at discharge from which it enters the external circuit. As you can see, the data contained in GOST 15596-82, consider the situation from a different position. Therefore, when consulting with other people about certain structures, you must be very careful.

The emergence of terms

They were introduced by Faraday in January 1834, to avoid confusion and to achieve greater accuracy. He also offered his own variant of memorizing with the example of the Sun. So, his anode is the sunrise. The sun moves upward (current enters). The cathode is a sunset. The sun moves down (current goes out).

Example of a radio tube and a diode

We continue to understand what to designate what is used. Let us assume that one of these energy consumers is available in the open state (in direct connection). Thus, an electric current flows from the external circuit of the diode into the element along the anode. But do not be confused by this explanation with the direction of the electrons. Through the cathode, an electric current flows out of the used element into the external circuit. The situation that has developed now, resembles the cases when people look at the inverted picture. If these designations are complex, remember that it is absolutely necessary for chemists to understand them. And now let's do the reverse inclusion. It can be noticed that semiconductor diodes will not conduct current practically. The only possible exception here is the reverse breakdown of the elements. And electrovacuum diodes (kenotrons, radiolamps) will not conduct a reverse current at all. Therefore, it is considered (conditionally) that he does not go through them. Therefore, the anode and cathode formally do not fulfill their functions in the diode.

Why is there confusion?

Specifically, to facilitate training and practical application, it was decided that the diode elements of the pin names will not change depending on their circuitry, and they will be "attached" to physical conclusions. But this does not apply to batteries. Thus, for semiconductor diodes, everything depends on the type of conductivity of the crystal. In electron tubes, this question is tied to an electrode that emits electrons at the location of the filament. Of course, there are certain nuances here: so, through such semiconductor devices as a suppressor and a zener diode, a reverse current can flow a little, but there is a specificity that clearly goes beyond the scope of the article.

We deal with the electric accumulator

This is a truly classic example of a chemical source of electric current that is renewable. The battery stays in one of two modes: charge / discharge. In both these cases there will be a different direction of electric current. But note that the polarity of the electrodes will not change at the same time. And they can perform in different roles:

1. During charging, the positive electrode receives an electric current and is an anode, and the negative electrode releases it and is called the cathode.
2. In the absence of movement about them, there is no point in talking.
3. During the discharge, the positive electrode releases the electric current and is the cathode, and the negative electrode receives and is called the anode.

On electrochemistry, say the word

Here, a few other definitions are used. Thus, the anode is considered as an electrode, where oxidizing processes occur. And remembering the school chemistry course, can you answer what is happening in another part? The electrode on which the reduction processes proceed is called the cathode. But there is no binding to electronic devices. Let's look at the value of oxidation-reduction reactions for us:

1. Oxidation. There is a process of recoil by a particle of an electron. The neutral turns into a positive ion, and the negative neutralizes.
2. Recovery. There is a process of obtaining a particle by an electron. The positive turns into a neutral ion, and then into a negative ion upon repetition.
3. Both processes are interrelated (for example, the number of electrons that are given is equal to their associated number).

Also Faraday for designation was introduced the names for the elements that take part in chemical reactions:

1. Cations. So called positively charged ions that move in the solution of the electrolyte towards the negative pole (cathode).
2. Anions. So called negatively charged ions that move in the electrolyte solution towards the positive pole (anode).

How do chemical reactions occur?

Oxidative and reduction half-reactions are separated in space. The transition of electrons between the cathode and the anode is not carried out directly, but due to the conductor of the external circuit, on which an electric current is created. Here one can observe the mutual transformation of the electrical and chemical forms of energy. Therefore, to form an external circuit, the system consists of conductors of various kinds (which are the electrodes in the electrolyte) and it is necessary to use the metal. You see, the voltage between the anode and the cathode exists, as well as one nuance. And if there was not an element that prevents them from directly producing the necessary process, then the value of the sources of the chemical current would be very low. And so, due to the fact that the charge must be walked on that scheme, the equipment was assembled and operated.

What is what: step 1

Now let's determine what is what. Take the galvanic element of Jacobi-Daniel. On the one hand, it consists of a zinc electrode, which is lowered into a solution of zinc sulfate. Then comes the porous septum. And on the other hand, there is a copper electrode, which is located in a solution of copper sulfate. They touch each other, but the chemical characteristics and the septum do not allow mixing.

Step 2: The Process

Oxidation of zinc occurs, and electrons along the outer chain move towards copper. So it turns out that the galvanic cell has an anode charged negatively, and the cathode is positive. Moreover, this process can only take place when the electrons have much to "go." The fact is that to get directly from the electrode to another prevents the presence of "isolation".

Step 3: Electrolysis

Let's look at the process of electrolysis. The installation for its passage is a vessel in which there is a solution or melt of the electrolyte. Two electrodes are omitted. They are connected to a direct current source. The anode in this case is an electrode that is connected to the positive pole. Here there is oxidation. A negatively charged electrode is a cathode. Here the reaction of reduction proceeds.

Step 4: Finally

Therefore, when operating these concepts, it is always necessary to take into account that the anode is not used in 100% of cases to designate a negative electrode. Also, the cathode can periodically lose its positive charge. It all depends on what process is on the electrode: a reducing or oxidizing one.

Conclusion

That's all it is - not very difficult, but you will not say that it's easy. We examined the galvanic cell, the anode and the cathode from the schematic point of view, and now you should not have problems connecting the power supplies with the operating time. And finally, you need to leave some more valuable information for you. It is always necessary to take into account the difference that the cathode potential / anode potential has . The fact is that the first will always be a little big. This is due to the fact that the efficiency does not work with the index of 100% and some of the charges are dissipated. It is because of this that you can see that the batteries have a limitation on the number of times the charge and discharge.