Electricity is a natural physical phenomenon. People first understood electricity through biological discharges such as lightning and electric rays/eels. It is recorded in the "Selected Medicines" of ancient Rome: By touching the electric stingray, patients may be cured of diseases such as gout and headaches by its powerful electric shock.
The first person to understand electricity in history was the Greek (Miletus). Through observation, he discovered that rubbing amber with a cloth would attract small objects such as feather lamps.
Systematic and scientific research on static electricity began in the 17th century. Several famous phenomena about static electricity were discovered in the 17th century: 1. Substances are divided into two categories: conductors and insulators (insulators are On the contrary, insulators can also become conductors under certain conditions);
2. Static electricity is generated at one end of a conductive object, and the static electricity can spread and distribute throughout the object;
3. Friction will produce two kinds of electricity (amber and glass friction produce different electricity). Objects with different kinds of electricity will attract each other, and objects with the same kind of electricity will repel.
People's understanding of electricity improved substantially in the 18th century. Franklin discovered the law of conservation of charge through experiments (in any isolated system, the total amount of electricity remains unchanged);
Coulomb passed the torsion balance Confirming Priestley's conjecture (the attraction between charged objects acting on each other obeys the same law as universal gravitation), he established the basic law of electrostatics - Coulomb's law (the attraction between two charged objects exerting on each other) Force is inversely proportional to distance). At this point, the study of electricity was elevated to an exact science.
Luigi Galvani created the academic field of bioelectricity through experiments with frogs connected to electrostatic generators to form closed circuits (discovering that nerve cells rely on the medium of electricity to transmit signals to muscles).
Alessandro Volta soaked copper and zinc sheets in salt water and connected them with wires to create the first battery: the Voltaic battery. Voltaic cells give scientists a more stable power source than electrostatic generators, capable of continuously supplying electric current.
The 19th century saw the vigorous development of electromagnetism, and electricity began to be widely used. The discovery of electromagnetic phenomena: Hans Oersted accidentally discovered during an experiment in class that electric current can deflect the direction of a compass, demonstrating how the current around the A magnetic field is generated, the magnetic effect of the electric current. André-Marie Ampere gave a quantitative description of this phenomenon, giving Ampere's force law and Ampere's law. (This is how electromagnets come about.)
Discovery of battery induction: Michael Faraday and Joseph Henry independently discovered that changes in magnetic fields can generate electric fields. James Maxwell integrated electromagnetism, proposed Maxwell's equations, and derived the electromagnetic wave equation. Since the speed of electromagnetic waves he calculated was equal to the measured speed of light, he boldly predicted that light waves were electromagnetic waves (in 1887, Heinrich Hertz successfully produced and received the electromagnetic waves described by Maxwell.). Later, Maxwell unified electricity, magnetism and optics into one theory.
Electrons were discovered: German physicist Julius Plucker discovered through homemade cathode rays that cathode rays propagate in straight lines, but their propagation direction is deflected by a magnetic field. Later, Joseph Thomson's experiments confirmed that cathode rays are composed of negatively charged particles called electrons.
The 19th century witnessed the rapid evolution of electromagnetism, which began to be gradually applied to real life, such as: 1. Bell invented the telephone; 2. Karl Braun improved the cathode ray tube, monitors, and televisions. Machines began to be born. 3. Edison invented the incandescent lamp and the DC power system; 4. Tesla invented the induction motor and alternating current; the emergence of many inventions related to electricity and magnetism made electricity the main driving force of the second industrial revolution and the modern era. Necessities of life.
In the 19th century, the competition between direct current represented by Edison and alternating current represented by Tesla began. Tesla first helped Edison with simple electrical design, but he was soon able to solve some very difficult problems. , and helped Edison improve DC motors. But Edison did not pay Tesla the $50,000 he had promised. Tesla left his job in anger to start a business, and with the help of Westinghouse Electric Company, he invented alternating current. When the power system began to be developed, there were two competing technical ideas. One was the DC school represented by Edison, and the other was the AC school represented by the Westinghouse Company.
The DC current always flows in the same direction and is transmitted to distant places. The DC current is easily converted into heat and lost, which will cause large-scale automatic power outages. The AC current repeatedly changes the flow direction at a certain frequency, which can be output externally. Electricity can be exported inward and even transmitted further.
Compared with DC power, AC power has less energy loss, and there is no need to install many power plants. As long as the voltage is raised during transmission, the voltage is lowered when it reaches the user's vicinity, the cost can be reduced. Therefore, many power plants later turned to Westinghouse, represented by AC power, and Edison's DC power was gradually ignored by the industry.
In the early days of electrical distribution systems, the DC transmission system was the standard in the United States, and Edison did not want to lose his patent royalties. The anxious Edison began to stigmatize alternating current, and designed the world's first electric chair that used high-voltage alternating current to execute prisoners, and electrocuted cats, dogs, horses and other animals alive in the crowd, leaving the public with no idea of ??alternating current. Make a dangerous impression.
In 1893, two companies, Edison and Westinghouse, bid for the "Columbus Memorial Exposition." The entire Exposition abandoned traditional kerosene lamps and switched to electric lighting. In the end, Westinghouse won the bid, and Tesla worked day and night to finally complete the construction of a large-scale AC power generation equipment to provide the entire exhibition venue's power needs. There were more than 100,000 spectators at the venue to witness the bright future of the new city, and all of them were amazed and amazed. After the fair, alternating current became more and more popular. The semiconductor era has forced the return of direct current. Since the magnitude and direction of direct current will not change, it is not periodic and will only flow in one direction at a fixed voltage. These are properties required of semiconductors so that transistors can maintain stable on and off states.
Transistors and DC have laid the foundation for the large-scale and miniaturization of circuits, and the return of DC is inevitable. Direct current and alternating current are products of the application of electromagnetic technology. At present, both direct current and alternating current have their own uses. Alternating current is suitable for long-distance transmission, and direct current is suitable for various electronic devices. Direct current and alternating current have dramatically transformed from the earliest incompatible current war to complementing each other, much like our lives.
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