Cathode and anode - unity and struggle of opposites

The cathode and the anode are two components of one process: the flow of electric current. All materials can be divided into two types - they are conductors, in the structure of which there is a large excess of free electrons, and dielectrics (there are practically no free electrons in them).

The concept of electric current

Electric current is the ordered movement of charged elementary particles in the structure of a substance under the influence of an electromagnetic voltage. If a constant voltage is applied to the conductor, free electrons having a negative charge will start to move in an orderly direction toward the anode (positively charged electrode) from the cathode (negatively charged electrode). The current, respectively, will flow in the opposite direction. A cathode and an anode are two electrodes, between which a difference (difference) in the electromagnetic voltage is formed.

Conductors and dielectrics

Conductors and dielectrics can be solid, liquid and gaseous substances. This is not essential for the flow of electric current. When the electromagnetic voltage is applied for a long time to the material, an excess of electrons will form on the cathode, and at the anode its shortage. If the voltage is applied for a sufficiently long time, the bound electrons together with the atoms will break out of the structure of the material from which the anode is made, and the material itself will begin to react chemically with the reactive substances from the environment. This process is called electrolysis.

Electrolysis

The cathode and anode in electrochemistry are the two poles of a permanent electromagnetic voltage applied to saline solutions or melts. When a current is generated from an excess of electrons, the anode begins to break down, i.e. The positively charged atoms of matter themselves will fall into the brine (the environment) and be transferred to the cathode, where it will settle in a purified form. This process is called galvanic. With the help of electroplating cover a thin layer of zinc, copper, gold, silver and other metals various products.

What is the cathode and what are the tasks that it performs in electrolysis? This can be understood by performing the following actions: if an anode is made of bronze or tin, then a printed circuit board, coated with a thin layer of copper or tin (used in the electronic industry), will be produced on the cathode. The same way get gilded jewelry, coppered and even gilded aluminum tips for electrical engineering in order to increase electrical conductivity.

Answers to the questions about what an anode and cathode are, in the electrolysis are obvious: the anode as a result of the flow of direct current through the brine is destroyed, and the cathode takes over the anode material. Even such a term arose in the environment of electroplating - "anodizing the cathode". It does not carry physical meaning, but it displays the actual essence of the matter beautifully.

Semiconductors

Semiconductors are materials that do not have free electrons in the structure, and atomic ones do not hold well in their places. If such a material is placed in a liquid or gaseous state in a magnetic field and then allowed to solidify, an electrically structured semiconductor will be obtained, which will flow the current only in one direction. From this material, using the above property, do diodes. They are of two types:

A) with "pnp" conductivity;

B) with "npn" conductivity.

In practice, this fineness of the structure of the diodes does not matter. It is important to connect the diode correctly. Where is the anode, where the cathode is a question that many are puzzled. On the diode there are special symbols: either A and K, or + and -. It is possible to connect the diode only in two ways to the DC electrical circuit. In one case, an operating diode will conduct a current, and in the other, it will not. Therefore, it is necessary to take the device, on which it is known, where the cathode is, and where the anode, and connect it to the diode. If the device shows the presence of current, the diode is connected correctly. Hence, the cathode of the device and the cathode of the diode, as well as the anode of the device and the anode of the diode coincided. Otherwise, you need to change the connections in places.

1. If the diode does not pass current in both directions, then it is burnt out, it can not be repaired.

2. If on the contrary, misses, then it is punched. It must be discarded.

Diodes are tested by testers and probes. In diodes, the cathode and anode are rigidly tied to their material design, unlike galvanic power sources (batteries, batteries , etc.).

The cathode in the semiconductor elements (diodes) of the electrical circuit is the electrode (leg) from which the positive (+) potential comes out. Through the circuit it is connected with the negative potential of the power source. This means that the current flows directly in the diode semiconductor from the anode to the cathode. On electrical circuits, this process is symbolically indicated.

If a diode is connected to an alternating voltage by one leg (electrode), then on the second electrode we get a positive or negative half-sine wave. If we connect the two diodes to the bridge, then we will observe a rectified electric practically constant current.

Galvanic DC sources - batteries (batteries)

The cathode and anode in these products change places depending on the direction of the current flow, because in one case the voltage does not come to them, and they themselves serve as sources of direct current due to the chemical reaction. Then the negative electrode will already be the anode, and the positive electrode is the cathode. In the other case, the usual electrolysis process takes place in the battery.

When the battery is discharged and the chemical reaction, which served as a source of electric current, stopped, it must be charged with an external power source. Thus, we start the process of electrolysis, i.e. Restore the original properties of the galvanic battery. At the cathode of the battery, it is necessary to apply a negative charge already, and on the anode - positive, then the battery will be charged.

Thus, the answer to the question of how to determine the cathode and anode in a galvanic cell depends on whether it is charged or serves as a source of electric current.

Conclusion

As a summation of the foregoing, the cathode is an electrode on which an excess of electrons appears, and the anode is an electrode on which a shortage of electrons appears. But plus or minus the specific electrode of the electrical circuit element is determined by the direction of the current flow.