Laws of Vietnam

The meter is the length of path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second (17 ^th CGPM*, 1983).

The base unit.

The steradian is a solid angle, which, having its vertex at the center of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.

The square meter is the area of a square with 1- meter sides.

1 ha = 0.01 km² = 10⁴ m²

The liter is the capacity equal to one cubic decimeter

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom the 13 ^th CGPM, 1967).

The hertz is the frequency of a periodic phenomenon occurring one cycle per second.

Radian per second is the angular velocity of an object rotating steadily around a fixed axis in an angle of 1 radian in 1 second.

Radian per second squared is the angular acceleration of an object with an angular velocity steadily changing one radian per second in 1 second.

Meter per second is the velocity of an object travelling 1 meter in one second.

Kilometer per hour is the velocity of an object travelling 1,000 meters in an hour

Meter per second squared is the acceleration of an object with a velocity steadily changing 1 meter per second in a second

The neper is the level of a field quantity when the ratio between this quantity and a compared quantity of the same kind is equal to e

The bel is the level of a field quantity when the ratio between this quantity and a compared quantity of the same kind is equal to 10^1/2

The neper is the level of a power quantity when the ratio between this quantity and a compared quantity of the same kind is equal to e²

The bel is the level of a power quantity when the ratio between this quantity and a compared quantity of the same kind is equal to 10

1 t = 1,000 kg

Kilogram per meter is the weight by length of a homogeneous object of even cross-section, which is 1 kilogram in weight and 1 meter in length.

Kilogram per square meter is the weight by surface of a homogeneous object of even thickness, which is 1 kilogram in weight and 1 square meter in area.

Kilogram per cubic meter is the specific weight of a homogeneous object which is 1 kilogram in weight and 1 cubic meter in volume.

Ton per cubic meter is the specific weight of a homogeneous object, which is 1 ton in weight and 1 cubic meter in volume.

Kilogram per liter is the specific weight of a homogeneous object, which is 1 kilogram in weight and 1 liter in volume.

The newton is a force which gives a mass of 1 kilogram an acceleration of 1 meter per second squared

Newton meter is the moment of a force of 1 newton to a point with a radius vector of 1 meter between that point and another point in the direction of the force.

The pascal is the pressure generated by a force of 1 newton applied perpendicularly over an area of 1 square meter

Pascal second is the dynamic viscosity of a homogeneous, isotropic liquid flowing in layers, when between two plane layers in parallel with the flow and 1 meter apart there is a velocity difference of 1 meter per second, and on the surface of these layers there appears a tangent stress of 1 pascal.

Square meter per second is the kinetic viscosity of a liquid having a dynamic viscosity of 1 pascal second and a specific weight of 1 kilogram per cubic meter.

The joule is the amount of work done when the point of application of 1 newton is displaced for a distance of 1 meter in the direction of the force.

The watt is the power which gives rise to the production of energy at the rate of 1 joule per second.

Cubic meter per second is the volume velocity for a substance of 1 cubic meter in volume to cross a given cross-section in a second.

Kilogram per second is weight velocity of a homogeneous flow for a substance of 1 kilogram in weight to cross a given section in 1 second.

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water (13^th CGPM, 1967).

Degree Celsius is the specific name of kelvin to denote the values of Celsius temperature

Joule per kilogram is the specific energy of a system of one kilogram in weight that obtains or emits an energy of 1 joule when being dissolved or completing a chemical reaction.

Joule per kelvin is the heat capacity of a system which needs an energy of 1 joule to increase its temperature one more kelvin.

Joule per kilogram kelvin is the specific heat capacity of a homogeneous object of 1 kilogram in a constant pressure or volume, which, when an energy of 1 joule is added, will increase the temperature by 1 kelvin.

The watt is the thermal flux to carry an energy of 1 joule in a second.

Watt per square meter is the surface thermal flux when a thermal flux of 1 watt running through each square meter of the surface.

Watt per square meter kelvin is the thermal conductivity co- efficient between two environments with a temperature difference of 1 kelvin and the surface thermal flux of the contact surface is 1 watt per square meter.

Watt per meter kelvin is the thermal conductivity of a homogeneous object containing a temperature difference of 1 kelvin between two parallel surfaces of 1 square meter placed 1 meter apart, which produces a thermal flux of 1 watt between these two surfaces.

Square meter per second is the thermal diffusivity of an environment where the isothermal surfaces at any point of time are parallel ones and in every second the temperature at such point of time fluctuates 1 kelvin when the temperature gradient changes 1 kelvin per meter on each meter of length in the direction perpendicular to the isothermal surfaces.

The ampere is that constant current, which, if maintained in two straight parallel conducting wires of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2. 10^-7 newton per meter of length (9^th CGPM, 1948).

The coulomb is the quantity of electricity transported in 1 second by a current of 1 ampere.

The volt is the difference of electric potential between two points of a conducting wire when a constant current of 1 ampere between those points dissipates a power of one watt.

Volt per meter is the strength of an electric field generating a force of 1 newton on an object having an electric quantity of 1 coulomb.

The ohm is the electric resistance between two points of an homogeneous conductor of the same temperature when between these two points there is an electric potential difference of one volt, which produces a constant current of 1 ampere

The siemens is the electric conductance of a conductor having the electric resistance of 1 ohm.

The coulomb is the electric flux passing through a closed surface surrounding an electric quantity of 1 coulomb.

Coulomb per square meter is the electric flux density in a flat capacitor having two plates of infinite width, put in parallel in vacuum and each square meter of such plate is charged with an electric quantity of 1 coulomb.

1W.h = 3.6 x 10³J = 3.6 kJ

The electronvon is the work done when an electric quantity equal to that of an electron passing in an electromagnetic field a distance between the two ends of which there is an electric potential difference of one volt.

1eV = 1.602 177 x 10^-19 J = 160.217 7 zJ

Ampere per meter is the magnetic field strength generated in vacuum by an electric current of 1 ampere passing through a straight conductor, of infinite length, of negligible circular cross-section, at points of a circle sharing the same axis with such conductor and having a circumference of 1 meter

The farad is the electric capacitance of a capacitor between the plates of which there appears a difference of potential of 1 volt when it is charged by an electric quantity of 1 coulomb.

The henry is the electromagnetic inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at a rate of 1 ampere per second,

The weber is the magnetic flux, linking a circuit of one turn, produces in it an electromotive force of 1 volt as it is reduced to zero at a uniform rate in a second.

The tesla is the magnetic flux density in a surface of one square meter caused by a uniform magnetic flux of 1 weber perpendicular to that surface.

The ampere is the magnetomotive force in a closed line linking to a conductor in which a current of 1 ampere is flowing through.

Volt ampere is the apparent power in a circuit section placed below an effective potential difference of 1 volt, in which a current of an effective intensity of 1 ampere is passing through.

The var is the resistance capacity in a pure inductance (or pure electric capacitance) circuit section placed below an effective potential difference of 1 volt, in which a current of an effective intensity of 1 ampere is passing through.

Watt per steradian is the radiant intensity of a uniform point source emitting a radiant flux of 1 watt in a solid angle of 1 steradian.

Watt per square meter steradian is the radiance in a given direction at a point above a surface a unit area of which has a radiant intensity of 1 watt per steradian and the area of the projection of such unit area on the surface perpendicular to such direction is 1 square meter.

Watt per square meter is the radiant capacity at a point above the surface, which radiates a radiant flux of 1 watt on 1 unit area of 1 square meter of such surface.

Watt per square meter is the illumination at a point above the surface, which radiates a radiant flux of 1 watt on 1 unit area of 1 square meter of such surface.

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10¹² hertz and that has a radiant intensity in that direction of 1/683 watt per steradian (16^th CGPM, 1979).

Candela per square meter is the luminance of a flat source of one square meter with a luminous intensity of one candela measured in a direction perpendicular to the source.

The lumen is the luminous flux emitted in a solid angle of 1 steradian by a uniform point source having an intensity of 1 candela.

Lumen second is the amount of light of a luminous flux of one lumen calculated in one second.

Lumen per square meter is the luminous capacity of a spherical source having a surface of 1 square meter in area, emitting a luminous flux of 1 lumen distributed evenly in all directions.

The lux is the illuminance of a surface receiving a luminous flux of one lumen evenly distributed on an area of one square meter of that surface.

Lux second is the illuminating amount corresponding to the illuminance of 1 lux in 1 second.

The reciprocal meter is the focus of an optical system having a focal length of 1 meter in a refractive environment equal to 1.

The diopter is another name of the reciprocal meter

Octa is the range between two frequencies when the ratio between the higher frequency and the lower frequency is 2.

Cubic meter per second is the periodic volume velocity in a homogeneous acoustic field at a cross-section of 1m² of an acoustic conductor, on which the particle velocity is 1 meter per second.

Joule per cubic meter is the acoustic energy density in an acoustic field having an energy of 1 joule evenly distributed in a volume of 1 m³.

Watt per square meter is the acoustic intensity in a plane sound wave when it transmits an acoustic energy of 1 joule across a surface of 1 square meter in a second.

Pascal second per cubic meter is the acoustic impedance of an acoustic transmission tube, in which the negative sine pressure of 1 pascal at any cross-section causes a volume velocity having a value of 1 cubic meter per second at such cross-section point.

The unified atomic mass unit is a mass equal to 1/12 of the mass of an atom of the nuclide 12C.

The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles (14^th CGPM, 1971).

In the solution of two substances A and B, the molar energy of substance A is:

and the molar energy of substance B is:

The becquerel is the radioactivity of a source of radiation in which the quotient of the expected value of the number of spontaneous nuclear displacements or isomeric displacements and the duration of time during which these displacements occur advances to the limit of 1/s.

The gray is the dose absorbed in a material quantity of 1 kilogram which receives an energy of 1 joule from ionizing radiations under constant energy flux conditions.

The sievert is the equivalent dose in a tissue quantity of 1 kilogram which receives an energy of 1 joule from ionizing radiations with a quality factor value of 1 with regard to the assessment of the equivalent dose against the biological effects of charged particles which produce the absorbed dose and their energy flux is constant.

The gray is a kerma in a material quality of 1 kilogram which receives a total initial kinetic energy of 1 joule freed by charged ionized particles under constant energy flux conditions.

Coulomb per kilogram is the exposure of the photonic ionizing radiation generated in 1 kilogram of air of ions of the same sign having a total charge of 1 coulomb when all electrons (positive and negative), freed by photons in the air, stop completely there and all of their energy flux remains in the air.

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