Volt

Volt

This data is reviewed by the project of data compilation and application of Science Encyclopedia of science popularization in China.

Volt is a special name named after the surname of the first Italian scientist in the world who discovered the principle of producing electric current by chemical method. In 1881, volt was first adopted as the unit of voltage by the International Electrotechnical Commission. In 1960, the 11th International Conference on Metrology decided to take volt as a special name of an export unit of the international system of units. As a unit of voltage, "international volt" is different from "absolute volt". The relationship between them is: 1 International volt = 1.00034 absolute volt. "International volt" was replaced by "absolute volt" in 1948.

definition

1 W power is consumed between two points carrying 1A constant current conductor, and the potential difference between these two points is 1 v. Volt can also be expressed as: 1V = 1W / A.

The unit of voltage is volt (volt for short). In the international system of units (SI), the symbol is V, that is, when the work done by the electric field force to move 1 Coulomb (c) positive charge from point a to point B is 1 joule (J), the voltage between a and B is 1V.

Sometimes, kilovolt (kV), millivolt (MV) and microvolt (μ V) are used as voltage units.

The origin of the name

In electricity, there are three units of electricity: ampere, ohm and volt. They are all named after the people who made great contributions to mankind. Among them, the unit name of potential difference "volt" is named after alexandro volt.

On February 18, 1745, Alessandro volt was born into a noble family in Milan, Italy. Since he was in school, he has been very interested in natural science. At the age of 24, he published an academic paper, which attracted the attention of academic circles. At the age of 29, he became a physics professor at the Royal College of Como. A few years later, he became president of Padua University.

Volt began the study of electricity very early. In 1780, a professor of anatomy in Italy happened to find that the frog's legs were connected with metal, so as long as the thunderstorm came, the frog's legs would spasm. A few years later, it was found that as long as the rings made of two different metals were connected with frog legs, spasm would also occur. After hearing this news, volt decided to uncover the secret of "frog experiment". After many experiments, volt made a new breakthrough and finally opened the door of electricity. Volt discovered that electricity could be generated without animals, and in 1800 showed the first one volt battery, also known as voltaic stack at that time. It's made of zinc and silver sheets stacked together, with a cloth soaked in salt water in the middle. Before long, volt made another improvement, putting copper and zinc in containers containing dilute sulfuric acid, and connecting several such containers to form "volt battery". The invention of volt battery has changed the face of electricity, provided scientists with a permanent current source, and provided people with the possibility of electric energy application. When the volt cell was introduced to Britain, many scientists continued to carry out experiments and observations, which promoted the birth of electrochemistry and the establishment of electromagnetic field theory. Later, volt invented potential sequence, electroscope, accumulator and starter, which made the research of electricity to a new level.

In order to commemorate Volt's great contribution in physics, people use his surname as the unit name of electromotive force, potential difference and voltage, and name it "volt" for short. Due to his outstanding scientific achievements, he was elected a member of the Royal Society of England and a member of the French Academy of Sciences.

Change value

Since January 1990, most countries in the world, including China, will revise their voltage and resistance unit benchmarks to more accurately reproduce the voltage unit volt and resistance unit ohm of Si. In China, the adjustment of volt reference is 8.9ppm and Ohm reference is 1.53ppm. Affected by this, other electrical parameters, such as current, AC voltage and power, should be adjusted accordingly. This world-wide work of benchmark modification has aroused great attention from the industrial, commercial, scientific and technological circles of various countries. A lot of work has been done in the field of standard metrology in various countries. Through publishing papers, holding lectures and other forms, they explained the theoretical guidance and practical operation measures to the relevant departments. In the middle of September 1989, the State Administration of metrology of China held a meeting of representatives of regional metrology bureaus and major scientific research institutes of metrology instruments in Chengdu to arrange the implementation measures of value modification in China. The voltage and Ohm reference values were proposed by the International Commission on Metrology (CIPM) and carried out under unified guidance. Under the leadership of the International Conference on Metrology (CGPM), the International Committee on metrology is responsible for guiding and supervising the work of the International Bureau of Metrology (BIPM), and holds regular meetings to establish the cooperation among national metrology institutions. The electrical Advisory Committee (CCE) is one of the eight professional advisory committees of the International Committee on metrology, which is responsible for the research of international electrical units and measurement standards. It puts forward suggestions on Revising the definition and value of units, so as to promote the correct definition, realization, maintenance and reproduction of Si and its derived units. According to its suggestion, the International Committee on Metrology can make a decision directly on the definition of electrical unit and its reproduction method, or submit it to the International Conference on metrology for approval. When necessary, CCE can organize a working group to conduct special research on a certain issue.

In view of the deviation between the volt and Ohm reference standards and SI units of international system of units, and the increasing dispersion between the standards of various countries, CCE decided to establish two working groups at the 17th meeting in 1986 to establish the standard of volt and Ohm reproduction by using Josephson effect and quantum Hall effect respectively And the determination of its physical constants. On the basis of extensive and precise work, the two working groups submitted their research reports to CCE in June 1988. The report focuses on the development of Josephson effect volt reference and quantized Hall effect ohm reference in recent years. According to the latest measurement results of Josephson constant and von Klitzing constant, new values of these two constants are proposed. CCE studied and discussed these two reports, and decided to recommend that all countries adopt the new Josephson constant and Kriging constant from January 1, 1990, so as to modify the current volt and Ohm reference values, and stipulate that all countries should apply Josephson effect and quantized Hall effect to establish volt and Ohm standards in the future. If they do not have the above-mentioned means, they should also compare their standards with the above-mentioned standards The measurement value is determined by comparison. The resolution was subsequently approved by the International Conference on metrology.

According to the new Josephson constant, the adjustment of volt reference in most countries is 8.065ppm; that in the United States is 9.246ppm; that in France is 6.741pm; and that in the Soviet Union is 3.565ppm. As shown in Figure 1. According to the specific situation of our country, the National Institute of Metrology decided that the voltage standard adjustment of our country is 8.9ppm.

Common voltage values

Induced voltage of TV signal on Antenna: about 0.1mv

Voltage to maintain bioelectrical current: about 1.2MV

Nominal voltage of alkaline battery: 1.5V

Voltage between two poles of silver oxide battery for electronic watch: 1.5V

Voltage of one lead-acid battery: 2V

The voltage between the two poles of the battery of the handset: 3.7V

Human safety voltage: not higher than 36V

Household voltage in Japan and some American countries: 110V

Voltage of home circuit: 220 V

Power circuit voltage: 380V

Voltage of trolley bus power supply: 550 ~ 600V

Working voltage of TV picture tube: above 10KV

Power grid voltage above the train: 25kV

The voltage between clouds of lightning: up to 1000kV

Chinese PinYin : Fu Te