First, let's take a look at the difference between the two. The direct current refers to the direction, the size is stable, does not change with time, and the other means that these two aspects will follow the time change, our usual power supply system will do cyclical changes. And they all have their own advantages and disadvantages, because of this, so they are suitable for the application.
The direction of DC power does not change with time, so it is relatively stable. Now there must be a functional feature in electronic equipment, that is, it must have good stability, and we will use this one here, so Need to use something else, a certain change between the two, and the magnetic field it produces is relatively stable, so it is often used in some important control systems, such as substations, mobile communication base stations, etc.
The voltage of the alternating current can be changed by the transformer, but the other one cannot be realized at one point. Therefore, in the long-distance power transmission, we adopt the type that will change, mainly because the cables are very long. When we learn physics, we will know that this will make its resistance very large and cause a lot of energy loss, so we must increase the output voltage, so that the loss can be reduced. Finally, the terminal can convert the high voltage into a suitable voltage through the transformer. In this way, we will adopt the high-voltage AC transmission mode on a large scale and long distance.