Alternating current is a current whose direction changes periodically from time to time, with an average current of zero during a period. Unlike direct current, which changes direction over time, direct current does not change periodically.
Normally the waveform of alternating current (AC for short) is a sinusoidal curve. AC can transmit electricity efficiently. But there are actually other waveforms used, such as triangular waves and square waves. The mains electricity used in everyday life is alternating current with a sinusoidal waveform.
"Direct Current" (DC), also known as "constant current". DC is the unidirectional flow or movement of charges, usually electrons. The current density varies with time, but usually moves in the same direction at all times. As an adjective, DC can be used for the reference voltage (its polarity never changes). In a direct current circuit, electrons form from the cathode, negative pole and negative magnetic pole and move towards the anode, positive pole and positive magnetic pole. However, physicists define direct current as movement from the positive pole to the negative pole.
Constant current means that neither the magnitude (voltage high or low) nor the direction (positive or negative) varies with time (within a relative range), as in the case of dry cells. Pulsating DC means that the direction (positive and negative) remains the same, but the size changes with time, for example: we get a typical pulsating DC after rectification with a diode at 50Hz, a pulsating DC at 50Hz with half-wave rectification, and a pulsating DC at 100Hz with full-wave or bridge rectification, they only become smooth DC after filtering (with inductors or capacitors), but of course there is still a pulsating component (called ripple coefficient), the size of which depends on the filtering effect of the filtering circuit.
The 220V AC we use at home, also known as sine wave AC, has a sinusoidal variation in polarity, and the positive and negative poles also vary, so there is no question of plugging it in backwards. Although there are no positive or negative poles in AC, it is divided into a fire wire and a zero wire. By fire wire, we mean that there is a 220v voltage difference with earth.
As we now use alternating current in our homes, we can disregard positive and negative polarity when wiring led lights, but for safety reasons we recommend that the installation is carried out by a professional.
