Identify DC and AC

Alternating current (AC) is a type of electricity that changes both in size and direction over time.
Alternating current (AC) is triggered by an alternating current generator. in the power generation process, many pairs of magnetic poles are evenly distributed in a circle at a certain angle. In this way, each coil is cut into the magnetic line during the power generation process, because there are many pairs of magnetic poles, the voltage and current produced by the split of the magnetic lines produced by each pair of magnetic poles change according to the law of the string, so it can continuously generate stable electric streams. The alternating current frequency is generally 50Hz, that is, 50 changes per second. of course there are other frequencies. for example, electronic lines contain square waves and triangles, but the alternating current of these waveforms is not produced by the conductor cutting magnetic lines, but by the capacitor charging and discharging and Switching Transistor working.
The direction of direct current does not change with time. It is usually divided into DC and steady current. Pulsating DC has AC components, such as the voltage of about 300 volts in the power circuit of the color TV is the pulsating DC components can be removed by capacitor. Steady Current is ideal, with both the size and direction unchanged.
The most essential difference is:
Alternating current changes according to the sine curve. due to the fact that many pairs of magnetic poles are evenly distributed in a circular area at a certain angle during the power generation process of an alternating current generator, they are complementary when each magnetic pole is cut out during the power generation process, therefore, it can continuously generate stable current. The AC frequency is generally 50Hz, that is, 50 changes per second. of course there are other frequencies.
DC does not change according to the sine curve. There is no frequency change.
The most intuitive difference between alternating current and direct current is that the direction changes unchanged. The current direction of direct current does not change at any time, but the size may change; the most special direct current is the constant current at the same size direction. The so-called AC refers to the alternating current flow, and its direction changes alternately. The most common is the civil electricity, which is the positive (remainder) string alternating current, common electronic circuits include square wave current.

If the current size and direction do not change with time, is this current called dc?

If the current size and direction change over time, this current is called AC.

The full-wave rectified current is pulsating DC.

Zone-based traffic splitting and DC only need to grasp whether the direction changes with time. Even if the size changes with time, the AC/DC nature cannot be changed. For DC, what is the difference between "stable DC" and "Pulsating DC"? The size of the former does not change with time; the latter changes with time, however, their direction remains unchanged. This is the essence. Communication is easy to understand. You don't need to talk about it here.