In fact, strictly speaking, this "plug" is called a switching power adapter, and its purpose is to convert the alternating current from the power grid into direct current and transmit it to electronic equipment. The power adapter of the laptop is larger, and it is more convenient to warm hands in winter~
So why switch AC to DC? let's start from the beginning
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Electricity is a natural phenomenon. Static or moving charges can produce many interesting physical phenomena, such as lightning seen in thunderstorms and crackling sparks when you take off your sweater in winter. Later, scientists discovered laws from various electrical effects, so they invented batteries, generators, and electric motors.
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DC first, or AC first?
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220 volts/50 Hz alternating current is the power supply standard in our country, so many people think that all household appliances use alternating current. As for DC power, I can't think of anything else except the "DC inverter air conditioner" that will be chanted in the advertisement.
In fact, direct current is widely used, and you must have seen it and used it. for example:
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definition
Direct current is a current whose direction does not change with time.
Alternating current refers to the current that changes periodically in magnitude and direction.
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From the observation of the oscilloscope, one is straight and the other is curved...
Anyway, it’s all electricity, so there’s not much difference?
No~ No~ No~
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Let's turn to history and tell some gossip!
In 1884, with a letter of introduction from his former employer, a young man named Tesla hurriedly boarded a ship bound for the American Gold Rush. He was going to find his idol—Thomas Edison, hoping that he could help him complete the invention of the alternating current system.
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thomas edison
The letter reads:
"Dear Edison: I know two great men, one is you and the other is this young man."
At that time, Edison was selling his DC system to the world, and he was not optimistic about AC power at all. But with this letter, Tesla entered Edison's team as he wished.
Edison promised to pay him the equivalent of a million dollars in today's money if he solved the "DC generator and motor problem."
But when Tesla fixes Edison's machine and asks "What about the promised million?"
Edison actually laughed and said, "Tesla, you don't understand our American humor."
The idol in his heart collapsed, and Tesla, who was teased, left angrily and became an independent company. Since then, he has devoted himself to his AC system.
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Tesla and the AC Motor
At that time, Edison’s DC system required a power station for every square mile, and the transmission distance was very limited due to the excessive loss in the transmission process. Tesla’s AC system used thinner wires, higher voltage, less transmission loss and long transmission distance. Obviously, AC is more advantageous.
What did the underdog Edison do?
In order to "black" alternating current, Edison had a big brain hole. Bribe government officials to change the death penalty from hanging to electric shock.
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Alternating Current Electrocution Chair
They even hired children to electrocute stray cats and dogs with alternating current, in order to publicize that alternating current "is very dangerous".
Fortunately, Tesla firmly believed in the belief that "if you are dark or not, the alternating current is there", and through the lighting project at the Columbia Expo, it demonstrated the reliability and safety of alternating current, and finally won the "battle of electric currents" and returned its innocence.
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Aerial view of the Columbia World's Fair
Since then, alternating current has been recognized, replacing direct current, and has become the mainstream of power supply.
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AC or DC, who is better?
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As the line voltage continues to increase, the transmission power and transmission distance continue to increase, and direct current is favored by engineers again. Because direct current does not require rectification and filtering, there is no phase difference, and it is relatively stable. How does direct current step up?
To put it simply, the step-up work is done by the AC, and the AC-DC can be converted again. In addition, from the economic point of view, although the DC converter station is more expensive than the AC transmission substation, the DC line only needs two positive and negative lines, and the three-phase AC line needs three lines.
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example
At present, the transmission project with the highest voltage level in the world is the DC project - ±1100 kV Zhundong-South Anhui project. The total length of the project line is 3,324 kilometers, which is longer than the straight-line distance from Harbin to Haikou.
In the field of power transmission, generally more than 30 kilometers of underwater cables and asynchronous connections between two AC systems also use direct current.
Alternating current and direct current have their own characteristics. Some people make an analogy that alternating current is like a high-speed railway, and direct current is like an air plane. One can stop halfway, and the other can fly point-to-point. Which one to use depends on specific analysis of specific issues.
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Why do household appliances use direct current?
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Back to the field of home appliances, IT products (such as mobile phones, computers) and most home appliances use DC power inside. Because notebooks and mobile phones are required to be light, the rectifier is placed outside, while desktop computers, refrigerators, air conditioners, etc. put the rectifier inside the electrical appliance.
Why? Back to the essence, direct current flows continuously from positive to negative, while alternating current fluctuates. Electronic components work by identifying high and low potentials.
For example, a computer has a potential of 1 and a non-potential of 0, and the alternating current itself will have a zero-crossing potential, so that electronic components cannot make correct logical judgments.
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Electricity is an ever-evolving and complex subject, and this article obviously cannot detail every situation. However, if your girlfriend asks "Did you bring a charging plug for your phone?" you can calmly take out this article and correct it: "Honey, this is called a power adapter."
