The symbol of alternating current is "~", abbreviated as AC;
The symbol of direct current is "-",DC for short.
For example, the AC voltage is AC220V and the DC voltage is DC24V.
The magnitude and direction of alternating current alternate with periodically changing current at any time, and the average running value in a period is zero.
Direct current, also known as constant current, has the same magnitude and direction. The current density changes with time, and the direction of motion is always the same.
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Development history
When electromagnetic induction was discovered, the method of generating alternating current was known. The early products were developed by michael faraday, an Englishman, and Bo Piaorongsu, a Frenchman.
1882, British electrician James Gordon built a large two-phase alternator. Lord Kelvin and Sebastian Ferranti developed early alternators with frequencies ranging from 100 Hz to 300 Hz.
189 1 year, nikola tesla obtained the patent of "high frequency" (15000 Hz) alternator. 189 1 year later, power supply will be provided by multiphase alternator. Thereafter, the AC frequency of the alternator is usually designed between 16 Hz and 100 Hz, and it is used in conjunction with arc lamps, incandescent lamps or motors.
According to the law of electromagnetic induction, when the magnetic field around a conductor changes, an induced current will be generated in the conductor. Usually, the rotating magnet is called rotor, and the fixed group in the coil with conductor wound on the iron core is called stator. When it passes through a magnetic field, it will generate current. The basic machine for generating alternating current is called an alternator.
Sogou encyclopedia -DC
Sogou encyclopedia-alternating current
What are the voltages of alternating current and DC, and what symbols are used?
Alternating current: character code AC, graphic symbol ~ DC: character code DC, graphic symbol-AC voltage: symbol V~, domestic power frequency voltage 220 volts. DC voltage: symbol V-, pulsating DC refers to the continuous DC with fluctuating current, that is, the DC with varying current size, which is not necessarily periodic, and the small value is not necessarily zero.
Pulse DC refers to a single or periodic DC with a very short duration (milliseconds-microseconds). Often used to trigger other circuits.
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In DC circuit, electrons are formed from cathode, negative electrode and negative electrode and move to anode, positive electrode and positive electrode. However, physicists define direct current as the movement from the positive electrode to the negative electrode. On the contrary, in most countries, the current flowing out of the equipment is alternating current. Alternating current can be converted into direct current through a power supply consisting of a converter, a rectifier (to prevent current from flowing in the opposite direction) and a filter (to eliminate jitter in the current flowing out of the rectifier).
In fact, all electronic and computer hardware needs direct current to work. Most solid-state devices require voltages ranging from 1.5 to 13.5 volts.
The demand for current ranges from near zero in electronic watches to over 100 amps required by wireless communication energy amplifiers. Devices that use vacuum tubes, such as high-energy radio or television broadcasting transmitters or cathode ray tube (CRT) displays, all need about 150 volts to several thousand volts of direct current.