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What are the seven basic physical quantities in the international system of units
Length m
Mass kg
Time s
Current a
Thermodynamic temperature K
Luminous intensity CD
Amount of substance
What are the definitions of the seven basic physical quantities in the international system of units
Length: M
1. In May 1790, a special committee composed of French scientists suggested that one fourth of the total length of the meridian of the earth passing through Paris should be taken as the unit of length - meter
2. The 11th International metrology Congress in 1960: "the length of meter is equal to 1650 763.73 times of the wavelength of the transition between 2p10 and 5d1 levels of krypton-86 atom in vacuum."
3. The 17th International Conference on Metrology held in Paris in October 1983: "meter is the length of light travel in vacuum in a time interval of 1 / 299792458 seconds"
Mass: kg
The mass of 1000 cubic centimeters of pure water at 4 ℃,
Time: seconds (s)
In 1967, the 13th International Conference on weights and measures adopted a resolution to replace the astronomical definition of second with the following definition: one second is the duration of 9192631770 cycles of transition radiation between two hyperfine energy levels in the ground state of cesium-133 atom
International Atomic Time is an international reference time scale according to the definition of the second above, belonging to the international system of units (SI)
Current: Ampere (a)
Ampere is a constant current. If it is kept in two infinite parallel straight wires with negligible circular cross-section and one meter apart in vacuum, the force generated between the two wires is equal to 2 × 10-7 newton per meter of length. This definition was approved at the Ninth International Conference on Metrology in 1948, and at the eleventh International Conference on Metrology in 1960, Ampere is officially adopted as one of the basic units of the international system of units. Ampere is named in memory of French physicist A. - M. ampere
Thermodynamic temperature: Kelvin (k)
Kelvin is one of the seven basic units in the international system of units (SI). With absolute zero (0k) as the lowest temperature, Kelvin stipulates that the temperature of the three-phase point of water is 273.16k, and 1K is equal to 1 / 273.16 of the temperature of the three-phase point of water. The relationship between the thermodynamic temperature T and the commonly used centigrade temperature T is t = t + 273.15, Because the freezing point of water is approximately equal to 273.15k, and the unit of thermodynamic temperature (k) is exactly the same as that of centigrade (℃). Kelvin was named in memory of British physicist Lord Kelvin
Luminous intensity: candela (CD)
Candela is the luminous intensity of a light source in a given direction. The light source emits monochromatic radiation with a frequency of 540 × 1012 Hz, and the radiation intensity in this direction is 1 / 683 watt per spherical degree
The 540 × 1012 Hz radiation wavelength is about 555nm, which is the most sensitive wavelength for human eyes
Quantity of matter - the physical quantity indicating the number of particles in a substance
Mole is the unit of physical quantity of matter (mol)
According to scientific determination, the number of C atoms contained in 12g 12C is 6.0220943 × 1023, which is expressed by the symbol Na, which is called Avogadro constant
The approximate value of Avogadro constant (NA) is 6.02 × 1023
Definition: the amount of a substance containing 6.02 × 1023 particles of Avogadro constant is 1 mole
What are the seven basic physical quantities in the international system of units
SI system: seven basic units: length m, time s, mass kg, thermodynamic temperature (Kelvin temperature) k, current unit a, light intensity unit CD (candela), mass mol
Among the units of physical quantities listed below, the basic mechanical unit of the international system of units is ()
A kg
B meter
C cattle
D seconds
This question may be multiple choice or single choice.
C. The full name is Newton
A is the unit of mass, B is the unit of length, and D is the unit of time
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- 13. In the international system of units, there are seven basic units. Which of them are involved in mechanics?
- 14. The basic unit of length commonly used in the world
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- 17. What is the unit and significance of specific heat capacity?
- 18. In the international system of units, the unit of time is seconds (s). What are the larger units? There are four vacancies altogether
- 19. For example, "L" R
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