How did electricity come from? What's the difference between DC and AC?

Electricity is a natural phenomenon. Static or moving charge will produce many interesting physical phenomena, such as lightning in thunderstorm weather, and the crackling sparks when taking off sweaters in winter. Later, scientists discovered laws from various electrical effects, and invented batteries, generators, and motors.

Why is the current divided into AC and DC? This is not a subjective division, but a division according to the characteristics of different currents. The earliest direct current was not generated by generators, but by batteries. In 1799, the physicist Volt made a galvanic cell out of salt water and tin zinc metal chips. There would be movement of electrons between the two gold metals, which produced direct current.

In 1801, the British chemist Humphrey Davy applied direct current to the platinum wire by using the method of galvanic cell, and the platinum wire gave off dazzling white light. Although the cost of this electric lamp was very high, and it was very easy to oxidize without inert gas protection, and it was scrapped in a few minutes, the prototype of the electric lamp had been born, and Edison had not been born that year.

Strictly speaking, Edison was not the first person to invent the electric lamp. Before Edison, about 20 people had invented the early electric lamp model. However, because the technology of vacuum pumping inside the electric lamp was not invented at that time, and the durability of the filament material still needs to be improved, commercial electric lamps have not been listed, and people can only use kerosene lamps.

When the technology became mature, Edison acquired patents and then promoted electric lamps to thousands of households, making himself famous. What does this have to do with direct current?

Edison built many DC power stations in the city in order to let residents use electric lights. In the early days, electric lights were powered by DC, which had a disadvantage. Assuming that Edison's DC power station is at position A, residents within a radius of 1km from position A can ensure normal power use, but the lights in residents' homes 1km away are often dim, because the 110V voltage generated by the DC generator is lost on the line after several kilometers of transportation, and the power to the user's home may be less than 60V. This is the disadvantage of DC power: it cannot be boosted, and power consumption is too much. But what could Edison do? The DC generators have been built. This problem occurs! So Edison built many power stations in the city to cover the city to solve this problem, which was also a helpless move.

When the shortcomings of direct current were exposed, alternating current began to rise.

The problem of power loss on the line was perfectly solved by combining alternating current with the transformer invented at that time. First, raise the voltage of 110V, and the current will decrease (P=UI) when the voltage rises. Then the thermal power generated on the circuit P=the square of the current multiplied by R will be much smaller than before. In other words, it is only necessary to build an AC power station in the city center, and then install transformers in each community to ensure the voltage stability. It is not necessary to build a DC power station in the city. So far, it is better to judge whether DC or AC is better.

Alternating current and direct current have their own characteristics. Some people, for example, say that alternating current is like a high-speed railway, while direct current is like an air plane, which can stop halfway and fly point-to-point.

At present, 220 V 50 Hz AC power is used for domestic use and 380 V for industrial use. In some countries, 110 V or 60 Hz AC is used for civil electricity. In addition to changing the voltage, sometimes the frequency of alternating current also needs to be changed. Usually, AC is converted into DC, and then DC is converted into AC of the required frequency.

Large electrical equipment generally uses AC power, while many household appliances and digital products in life use DC power although they are connected to AC power. In some circuits, both currents are used alternately. No one is more important than others, and each has its own use. Only when alternating current and direct current complement each other can we create a better life.