Those involved in practical electronics need to know about the anode and cathode of the power supply. What and how is it called? Why exactly? There will be an in-depth consideration of the topic from the point of view of not only amateur radio, but also chemistry. The most popular explanation is that the anode is the positive electrode and the cathode is the negative. Alas, this is not always true and incomplete. To be able to determine the anode and cathode, you must have a theoretical basis and know what and how. Let's look at this within the framework of the article.
Anode
Let's turn to GOST 15596-82, which deals with chemical current sources. We are interested in the information posted on the third page. According to GOST, the anode is the negative electrode of a chemical current source. That's it! Why exactly? The fact is that it is through it 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. It is advisable to carefully consider the pictures presented in the article if the content seems too complicated - they will help you understand what the author wants to convey to you.
Cathode
We turn to the same GOST 15596-82. positive electrodeA chemical current source is one from which, when discharged, it enters an external circuit. As you can see, the data contained in GOST 15596-82 consider the situation from a different perspective. Therefore, one must be very careful when consulting with others about certain constructions.
The emergence of terms
They were introduced by Faraday in January 1834 to avoid ambiguity and achieve greater accuracy. He also offered his own version of memorization using the example of the Sun. So, his anode is sunrise. The sun moves up (current enters). The cathode is the entrance. The sun is moving down (current is going out).
Example of tube and diode
We continue to understand what is used to denote what. Suppose we have one of these energy consumers in the open state (in direct connection). So, from the external circuit of the diode, an electric current enters the element through the anode. But don't get 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 is reminiscent of cases when people look at an inverted picture. If these designations are complex, remember that only chemists must understand them in this way. Now let's do the reverse. It can be seen that semiconductor diodes will practically not conduct current. The only possible exception here is the reverse breakdown of elements. And electrovacuum diodes (kenotrons,radio tubes) will not conduct reverse current at all. Therefore, it is considered (conditionally) that he does not go through them. Therefore, formally, the anode and cathode terminals of the diode do not perform their functions.
Why is there confusion?
Specially, to facilitate learning and practical application, it was decided that the diode elements of the pin names will not change depending on their switching scheme, and they will be "attached" to the physical pins. But this does not apply to batteries. So, for semiconductor diodes, everything depends on the type of conductivity of the crystal. In vacuum tubes, this question is tied to the electrode that emits electrons at the location of the filament. Of course, there are certain nuances here: for example, a reverse current may flow through semiconductor devices such as a suppressor and a zener diode, but there is a specificity here that is clearly beyond the scope of the article.
Dealing with the electric battery
This is a truly classic example of a chemical source of electricity that is renewable. The battery is in one of two modes: charge / discharge. In both of these cases, there will be a different direction of electric current. But note that the polarity of the electrodes will not change. And they can act in different roles:
- During charging, the positive electrode receives the electric current and is the anode, while the negative electrode releases it and is called the cathode.
- If there is no movement, there is no point in talking about them.
- Duringdischarge, the positive electrode releases the electric current and is the cathode, while the negative electrode receives and is called the anode.
Let's say a word about electrochemistry
Slightly different definitions are used here. Thus, the anode is considered as an electrode where oxidative processes take place. And remembering the school chemistry course, can you answer what is happening in the other part? The electrode on which the reduction processes take place is called the cathode. But there is no reference to electronic devices. Let's look at the value redox reactions have for us:
- Oxidation. There is a process of recoil of an electron by a particle. The neutral turns into a positive ion, and the negative is neutralized.
- Restoration. There is a process of obtaining an electron by a particle. A positive turns into a neutral ion, and then into a negative when repeated.
- Both processes are interconnected (for example, the number of electrons that are given away is equal to their number added).
Faraday also introduced names for the elements that take part in chemical reactions:
- Cations. This is the name of positively charged ions that move in the electrolyte solution towards the negative pole (cathode).
- Anions. This is the name of negatively charged ions that move in the electrolyte solution towards the positive pole (anode).
How do chemical reactions happen?
Oxidation and reductionhalf-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 electrical and chemical forms of energy. Therefore, to form an external circuit of the system from conductors of various kinds (which are the electrodes in the electrolyte), it is necessary to use metal. You see, the voltage between the anode and the cathode exists, as well as one nuance. And if there were no element that prevents them from directly carrying out the necessary process, then the value of the sources of chemical current would be very low. And so, due to the fact that the charge needs to go through that scheme, the equipment was assembled and works.
What is what: step 1
Now let's define what is what. Let's take a Jacobi-Daniel galvanic cell. On the one hand, it consists of a zinc electrode, which is immersed in a solution of zinc sulfate. Then comes the porous partition. And on the other side there is a copper electrode, which is located in a solution of copper sulfate. They are in contact with each other, but the chemical features and the partition do not allow mixing.
Step 2: Process
Zinc is oxidized, and electrons move along the external circuit to copper. So it turns out that the galvanic cell has a negatively charged anode and a positive cathode. Moreover, this process can proceed only in cases where the electrons have somewhere to "go". The point is to go directlyfrom 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 an electrolyte melt. Two electrodes are lowered into it. They are connected to a direct current source. The anode in this case is the electrode that is connected to the positive pole. This is where oxidation takes place. The negatively charged electrode is the cathode. This is where the reduction reaction takes place.
Step 4: Finally
Therefore, when operating with these concepts, it must always be taken into account that the anode is not used in 100% of cases to denote a negative electrode. Also, the cathode can periodically lose its positive charge. It all depends on what process is taking place on the electrode: reductive or oxidative.
Conclusion
That's how everything is - not very difficult, but you can't say that it's easy. We examined the galvanic cell, anode and cathode from the point of view of the circuit, and now you should not have problems connecting power supplies with operating time. And finally, you need to leave some more valuable information for you. You always have to take into account the difference that the cathode potential / anode potential has. The thing is, the first one will always be a little big. This is due to the fact that the efficiency does not work with an indicator of 100% and part of the charges is dissipated. It is because of this that you can see that batteries have a limit on the number of times they can be charged anddischarge.
