International System of Units

The International System of Units , abbreviated SI, also called the International Measurement System , is the heir to the old decimal metric system, so the SI is also known generically as the metric system .

One of the main characteristics of the International Measurement System is that its units are based on fundamental physical phenomena. SI units are the international reference for the indications of all measuring instruments, and to which they are referred through an uninterrupted chain of calibrations or comparisons.

The International System of Units consists of seven basic units , also called fundamental units , which define the corresponding fundamental physical quantities , which have been chosen by convention, and which allow expressing any physical quantity in terms or as a combination of them. The fundamental physical quantities are complemented by two more physical quantities, called supplementary .

By combining the basic units, the other units are obtained, called units derived from the International System, and which allow defining any physical quantity.

In the following Table, any physical quantity can be selected to access definitions, their measurement units expressed in the SI and their equivalence with other measurement systems.

– TABLE OF PHYSICAL MAGNITUDES –

Fundamental Physical Magnitudes
Length Mass Weather Electric current intensity Temperature Amount of matter Luminous intensity

 

 

Supplementary Physical Magnitudes
Flat angle Solid angle

 

International System of Units of Measurement (SI)

 

Derived Physical Magnitudes
Force Energy Power Pressure Dynamic or absolute viscosity Kinematic viscosity Surface
Volume Speed Acceleration Density Volumetric flow rate Mass Flow Density
Mass Flow
Electric Charge Electrical capacity Electric resistance Electric conductivity Thermal transmittance Luminous flux Illuminance
Luminance Luminous Efficiency or Performance Frequency Period Irradiance Irradiation Electric Tension
Moment of Strength Thermal conductivity Thermal resistance Thermal Conductance Specific Heat Heat capacity Magnetic induction
Magnetic flux Magnetic Permeability          
 

 

International System of Units of Measurement (SI)

 

Other Utilities
Table of Multiples and Submultiples Unit converter English system Physical constants
 

 

International System of Units of Measurement (SI)

FUNDAMENTAL PHYSICAL MAGNITUDES

Length

International System Basic Unit (SI): meter ( m )

Definition : One meter ( m ) is defined, according to the General Conference of Weights and Measures, by setting the numerical value of the speed of light in vacuum, c , at 299 792 458 , when expressed in the unit ms -1 , where the second is defined based on the frequency of cesium 133, Δν Cs .

From the exact relationship c = 299 792 458 m · s -1 the following expression for the meter is obtained, expressed as a function of the constants  c  and  Δν Cs :

The result of this definition is that the meter is the length of the path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second.

Equivalences :

1 Amstrong (Å) = 10 -10 m

1 nanometer (nm) = 10 -9 m

1 Thou (thou) = 2.54 x 10 -5 m

1 pixel (px) = 0.000264583 m (0.264583 mm)

1 inch (inch, in) = 0.0254 m (25.4 mm)

1 foot (foot, ft) = 12 in = 0.3048 m

1 yard (yard, yd) = 3 ft = 36 in = 0.9144 m

1 rod = 1 perch = 5.5 and d = 5.0292 m

1 mile (mile, mi) = 1609.34 m

1 nautical mile = 1852 m

1 breaststroke = 1.83 m

1 league = 4828.03 m

1 light year = 9.46 x 10 15 m

 

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Mass

International System Basic Unit (SI): kilogram ( kg )

Definition : The kilogram ( kg ) is defined by setting the numerical value of the Planck constant, h , to 6,626 070 15 × 10 -34 , when expressed in the unit  J · s , equal to  kg · m 2 · s – 1 , where the meter and the second are defined as a function of  c  and  Δν Cs .

From the exact relation  h = 6,626 070 15 × 10 -34 kg · m 2 · s -1 we obtain the unit  kg · m 2 · s -1 , and from this the expression for the kilogram as a function of the value of the constant of Planck h :

From here, together with the definitions of the second and the meter, we obtain the definition of the unit of mass based on the three constants  h ,   Δν Cs  and  c :

As a result of this definition, the unit kg · m 2 · s -1 is defined  (the unit of the physical quantities of action and angular momentum). Together with the definitions of the second and the meter, this leads to the definition of the unit of mass as a function of the value of the Planck constant, h .

Previously, to define the kilogram as the SI unit of mass, reference was made to a certain existing pattern. In this way, the kilogram was defined as the mass equal to that of a cylinder 39 mm in diameter and height, made of an alloy of 90% platinum and 10% iridium, which is located at the International Bureau of Weights and Measurements, in Sèvres, France.

Equivalences :

1 ounce (ounce, oz) = 0.02834952 kg

1 pound (pound, lb) = 0.4535924 kg

1 metric ton (t) = 1000 kg

1 short ton (ton short, tn) = 907.1847 kg

1 long ton (long) = 1016,047 kg

1 gram (g) = 1.000010 -3 kg

1 arroba (a) = 11.5 kg

1 stone (st) = 6.350293 kg

1 metric quintal = 100 kg

1 American short hundredweight = 45,359237 kg

1 British long hundredweight (Long hundredweight) = 50.80234544 kg

1 drachma avoirdupois = 1.7718451953125 g

1 troy drachma = 3.8879346 g

1 grain (gr) = 0.06479891 g

 

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Weather

International System Basic Unit (SI): second ( s )

Definition : The second ( s ) is defined by setting the numerical value of the frequency of the hyperfine transition of the undisturbed ground state of the cesium 133 atom, Δν Cs , at 9 192 631 770 , when expressed in the Hz unit, equal a s -1 .

From the exact relationship  Δν Cs = 9 192 631 770 s -1   , the expression for the second unit is obtained, based on the value of Δν Cs :

As a result of this definition, the second can also be defined as the duration of  9 192 631 770  periods of radiation corresponding to the transition between the two hyperfine levels of the undisturbed ground state of the cesium 133 atom, at a temperature of 0 K .

 

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Electric current intensity

International System Basic Unit (SI): amp ( A )

Definition : The ampere ( A ) is defined by setting the numerical value of the elementary charge, e , to 1,602 176 634 × 10 -19 , when expressed in unit  C , equal to  A · s , where the second is defined in function of  Δν Cs .

From the exact relationship  e = 1,602 176 634 × 10 -19 A · s   the expression for the unit ampere is obtained as a function of the constants  e  and  Δν Cs :

The effect of this definition is that the ampere can also be defined as the electric current corresponding to the flow of  1 / (1,602 176 634 × 10 -19 ) = 6,241 509 074 × 10 18   elementary charges per second.

Previously to this given definition, an ampere could also be defined as the intensity of a constant current between two parallel, rectilinear conductors, of infinite length, of negligible circular section and located between them at a distance of 1 meter in vacuum, which would produce a force equal to  2 × 10 -7 newton per meter (N / m) of conductor length.

 

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Temperature

International System Basic Unit (SI): kelvin ( K )

Definition : The kelvin ( K ) is defined by setting the numerical value of the Boltzmann constant, k , to 1,380 649 × 10 -23 , when expressed in the unit  J · K -1 , equal to  kg · m 2 · s -2 · K -1 , where the kilogram, meter and second are defined as a function of  h , c  and  Δν Cs .

From the exact relationship  k = 1,380 649 × 10 -23 kg · m 2 · s -2 · K -1 the expression for the kelvin is obtained as a function of the constants  k , h  and  Δν Cs :

The effect of this definition is that the kelvin equals the thermodynamic temperature variation resulting in variation of thermal energy kT of 1.380 649 × 10 -23 J .

Prior to this definition, the kelvin was also defined as the 1 / 273.16 fraction     of the thermodynamic (or absolute) temperature of the triple point of water ( 273.16 K ).

Equivalences :

Temperature in degrees Celsius, ºC = K – 273.15

 

Temperature in degrees Fahrenheit, ° F = 9  K – 459.67
5

 

  ºF – 32  
Temperature in degrees Celsius, ºC =  
  1.8  

 

 

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Amount of matter

International System Basic Unit (SI): mol ( mol )

Definition : One mole contains exactly   6,022 140 76 × 10 23   elemental entities. This figure is the fixed numerical value of the Avogadro constant, A , when expressed in the unit mol -1 , and is called the Avogadro number.

The amount of substance, symbol n , of a system is a measure of the number of specified elemental entities. An elemental entity can be an atom, a molecule, an ion, an electron, or any other specified particle or group of particles.

From the exact relationship  A = 6,022 140 76 × 10 23 mol -1 , the mol is obtained as a function of the constant A :

The effect of this definition is that the mole is the amount of substance in a system that contains 6,022 140 76 × 10 23 specified elemental entities.

Another definition of mol is the number of elemental units (atoms, molecules, ions, etc.) in a material system that is equal to the number of atoms existing in 12 grams of the carbon-12 isotope. This quantity of elemental units is a constant that does not depend on the type of material of value  6.022 140 76 × 10 23 , and is known as Avogadro’s Number.

 

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Luminous intensity

International System Basic Unit (SI): candela (cd)

Definition : The candle is defined by setting the numerical value of the luminous efficacy of the monochromatic radiation of frequency  540 × 10 12 Hz, cd , at 683 , when it is expressed in the unit  lm · W -1 , unit equal to  cd · Sr · W -1 , or a  cd · sr · kg -1 · m -2 · s 3 , where the kilogram, meter and second are defined as a function of  h , c  and  Δν Cs .

From the exact relationship  K cd = 683 cd · sr · kg -1 · m -2 · s 3 the expression for the candle is obtained:

or, expressing kg, mys based on the constants  h  and  Δν Cs :

The effect of this definition is that the candle is the light intensity, in a given direction, of a source that emits monochromatic radiation of frequency  540 × 10 12 Hz and has a radiant intensity in that direction of ( 1/683 ) W / sr (watts per stereoradian).

Therefore, the candle, as the International System unit of measure for light intensity, is understood as the luminous flux emitted per unit of solid angle in a specific direction.

Symbol : I

Equivalences :

I = Φ
Ω

 

where:

I is the light intensity, measured in candles.

Φ is the luminous flux, in lumen.

Ω is the solid angle differential element, in steradians.

 

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SUPPLEMENTARY PHYSICAL MAGNITUDES

Flat angle

International System Basic Unit (SI): radián (rad)

Definition : a radian is the angle that limits an arc of circumference whose length is equal to the radius of the circumference.

Equivalences :

1 degree (°) = π / 180 rad = 0.01745329 rad

1 ‘(minute) = π / (1.08 · 10 4 ) rad = 0.0002908881 rad

1 ” (second) = π / (6.48 · 10 5 ) rad = 4.848135 · 10 -6 rad

1 turn or revolution (r) = 2 · π rad = 6.283184 rad

 

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Solid Angle

International System Basic Unit (SI): estereorradián (sr)

Definition : the stereoradian is the solid angle that, having its vertex in the center of a sphere, delimits on the spherical surface corresponding to an area equal to that of a square whose side is the radius of the sphere.

 

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DERIVED PHYSICAL MAGNITUDES

Force

International System Basic Unit (SI): Newton (N)

Definition : a newton is the force necessary to provide an acceleration of 1 m / s 2 to an object whose mass is 1 kg.

N = kgm / s 2

Equivalences :

1 kilopond or kilogram-force (kp) = 9.80665 N

1 dyna (dyn) = 1.000010 -5 N

1 poundal (pdl) = 0.13825495 N

1 ounce-force (ozf) = 0.2780139 N

1 pound-force (lbf) = 4.448222 N

 

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Energy

International System Basic Unit (SI): July (J)

Definition : a july represents the energy required to move an object a distance of one meter by applying a force of one newton; that is, it is a magnitude of force per distance.

J = N · m = (kg · m / s 2 ) · m = (kg · m 2 ) / s 2

Other definitions of the July unit :

  • a july represents the kinetic energy (movement) of a body with a mass of two kilograms, moving with a speed of one meter per second (m / s) in a vacuum: E c= 0.5 · m · v two
  • A july represents the work required to move an electric charge from a coulomb through a voltage (potential difference) of one volt. That is, one volt-columbium (V · C). This relationship can be used, in turn, to define the unit volt.
  • One July represents the work required to produce one watt (watt) of power for one second. That is, one watt-second (W · s). This relationship can also be used to define the watt.

Equivalences :

1 Nm = 1.0 J

1 W · s = 1.0 J

1 dyn · cm = 1,0 · 10 -7 J

1 kpm = 9.8067 J

1 electronvolt (eV) = 1.6021910 -19 J

1 erg (erg) = 10 -7 J

1 calorie (cal) = 4.1868 J

1 kWh = 3.600010 6 J

1 atm · l = 101.29 J

1 PS · h = 2,6478 · 10 6 J

1 British Thermal Unit (Btu) = 1.055110 3 J

1 Chu = 1,899110 3 J

1 ft · pdl = 4.2139 · 10 -2 J

1 ftlbf = 1.3558 J

1 hp · h = 2.6845 · 10 6 J

1 therm = 1.055110 8 J

1 Thermia = 4,18710 6 J

 

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Power

International System Basic Unit (SI): watt (W)

Definition : A watt is the power that generates an energy of one July per second. In electrical terms, a watt is the power produced by a potential difference of one volt and an electric current of one ampere.

W = J / s = V · A = (m 2 · kg) / s 3

Equivalences :

1 kp · m / s = 9.80665 W

1 kcal / h = 1.1630 W

1 erg / s = 1,000010 -7 W

1 CV = 735.49875 W

1 PS = 7.354810 2 W

1 HP = 745.69987 W

1 BTU / s = 1054,118 W

1 BTU / h = 0.2928104 W

1 ftlbf / s = 1.3558 W

1 frigoria / h = 1.1630 W

1 ton refrigeration = 3.516910 3 W

1 therm / hr = 2.930810 4 W

 

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Pressure

International System Basic Unit (SI): Pascal (Pa)

Definition : a pascal is the normal (perpendicular) pressure that a force of one newton exerts on a surface of one square meter.

Pa = N / m 2 = kg / (s 2 · m)

Equivalences :

1 N / mm 2 = 10 6 Pa

1 bar = 10 5 Pa

1 atmosphere (atm) = 1.013310 5 Pa

1 kp / cm 2 = 9.806710 4 Pa

1 Torr = 1.333210 2 Pa

1 mmHg = 1.333210 2 Pa

1 mca (meter of water column) = 9806.65 Pa

1 dyn / cm 2 = 1,000010 -1 Pa

1 pdl / ft 2 = 1,4881 Pa

1 lbf / ft 2 = 47.88026 Pa

1 lbf / in 2 or PSI = 6.894810 3 Pa

1 in water = 2,490910 2 Pa

1 ft water = 2,989110 3 Pa

1 inHg = 3.386610 3 Pa

1 ton / in 2 = 1.379010 7 Pa

1 ton / ft 2 = 9.576110 4 Pa

 

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Dynamic or absolute viscosity

International System Basic Unit (SI): kg / (ms), or N · s / m² (Pa · s)

Definition : The dynamic or absolute viscosity measures the internal resistance of a fluid to flow, or in other words, quantifies the degree of opposition of a fluid to tangential deformations. The dynamic viscosity of 1 Pa · s for a homogeneous fluid, in which, when there is a speed difference of one meter per second between two parallel planes separated by one meter, the rectilinear and uniform movement of a flat surface of one square meter causes a retarding force of one newton.

Equivalences :

1 poise (P) = 0.1 Pa · s

1 centipoise (cP) = 10 -3 Pa · s

1 kps / m 2 = 9.80665 Pa · s

1 kph / m 2 = 3,532 · 10 -4 Pa · s

1 lb / (ft · h) = 4.1338 · 10 -4 Pa · s

1 kg / (m · s) = 1,0000 Pa · s

1 Reyn = 6,89010 3 Pa · s

 

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Kinematic viscosity

International System (SI) Basic Unit: m 2 / s

Definition : Kinematic viscosity is defined as the ratio of the absolute viscosity to the density of the fluid.

Equivalences :

1 stokes (St) = 10 -4 m 2 / s

1 centistokes (cSt) = 10 -6 m 2 / s

1 dm 3 / hrin = 1.093610 -5 m 2 / s

1 ft 2 / h = 2.580610 -5 m 2 / s

1 ft 2 / s = 9.290310 -2 m 2 / s

 

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Surface

International System Basic Unit (SI): square meter (m 2 )

Definition : a square meter is the area equivalent to that of a square of one meter per side.

Equivalences :

1 in 2 = 6.451610 -4 m 2

1 ft 2 = 9.290310 -2 m 2

1 yd 2 = 8.361310 -1 m 2

1 acre = 4.046910 3 m 2

1 mile 2 = 2.590010 6 m 2

1 area = 100 m 2

1 hectare (ha) = 10000 m 2

1 b (barnio) = 1,000010 -28 m 2

 

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Volume

International System Basic Unit (SI): cubic meter (m 3 )

Definition : one cubic meter is the volume of a cube of one meter of edge.

Equivalences :

1 liter = 1 dm 3 = 1,000010 -3 m 3

1 in 3 = 1,638710 -5 m 3

1 ft 3 = 2.831710 -2 m 3

1 yd 3 = 7.6455 · 10 -1 m 3

1 US gal = 3.785310 -3 m 3

1 UK gal = 4.546010 -3 m 3

1 US bushel (dry) = 3.523910 -2 m 3

1 UK bushel (dry) = 3.636910 -2 m 3

1 barrel (petroleum US) = 1.589810 -1 m 3

1 lube oil barrel = 2.081910 -1 m 3

1 bucket = 2.3659 · 10 -4 m 3

1 gill = 1.182910 -4 m 3

1 register ton = 100 ft 3 = 2.8317 m 3

1c = 8 UK bushels = 32 pecks = 64 Uk gallons = 256 quarts = 512 pints = 0.2909 m 3

 

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Speed

International System Basic Unit (SI): meter / second (m / s)

Definition : one meter per second is the speed of a body that, with uniform movement, travels a length of one meter in one second.

Equivalences :

1 km / h = 0.2778 m / s

1 ft / h = 8.466710 -5 m / s

1 ft / min = 5.0800 · 10 -3 m / s

1 ft / s = 3.048010 -1 m / s

1 mile / h = 4.470410 -1 m / s

1 knot = nautical mile / h = 0.5144 m / s

1 mach = 3,3146 · 10 2 m / s

1 c (speed of light) = 2.997910 8 m / s

 

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Acceleration

International System Basic Unit (SI): meter / second 2 (m / s 2 )

Definition : is the increase that a body experiences its speed in the amount of one meter per second every second.

Equivalences :

1 g = 9.80665 m / s 2

1 ft / s 2 = 0.3047987 m / s 2

 

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Density

International System Basic Unit (SI): kilogram / meter 3 (kg / m 3 )

Definition : is the amount of mass (kg) contained in each cubic meter of volume. Or put another way, it is the relationship between the mass of a body and the volume it occupies.

Equivalences :

1 grain / ft 3 (gr / ft 3 ) = 2,288410 -3 kg / m 3

1 lb / ft 3 = 16.01846 kg / m 3

1 lb / in 3 = 2,7679910 4 kg / m 3

1 ton / yard 3 = 6.93592510 2 kg / m 3

1 lb / UKgal = 99,779 kg / m 3

1 lb / USgal = 1.1383 · 10 2 kg / m 3

 

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Volumetric flow rate

International System Basic Unit (SI): meter 3 / second (m 3 / s)

Definition : is the amount of fluid (volume) that passes through a given area in the unit of time.

Equivalences :

1 ft 3 / hour (ft 3 / h) = 7.865810 -6 m 3 / s

1 ft 3 / min (ft 3 / min) = 4.719510 -4 m 3 / s

1 US gal / hour = 1.051510 -6 m 3 / s

1 UK gal / hour = 1.262810 -6 m 3 / s

1 barrel / day (petroleum US) = 1.840110 -6 m 3 / s

1 US gal / min = 6.3089 · 10 -5 m 3 / s

1 UK gal / min = 7.576610 -5 m 3 / s

1 mgd = 5.261710 -2 m 3 / s

 

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Mass Flow

International System Basic Unit (SI): kilogram / second (kg / s)

Definition : corresponds to the mass flow of a substance such that a quantity of 1 kilogram of mass passes through a determined section in 1 second.

Equivalences :

1 pound / hour (lb / h) = 1.260010 -4 kg / s

1 ton / day (short) = 1.050010 -2 kg / s

1 ton / day (long) = 1.176010 -2 kg / s

1 ton / hour (short) = 2,5200 · 10 -1 kg / s

1 ton / hour (long) = 2.822410 -1 kg / s

 

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Mass Flow Density

International System Basic Unit (SI): kilogram / meter 2 second (kg / m 2 s)

Definition : represents the amount of mass of a substance that crosses the unit of area per unit of time.

Equivalences :

1 pound / hour · foot 2 (lb / hft 2 ) = 1.356210 -3 kg / m 2 s

1 kilogram / hour · foot 2 (kg / hft 2 ) = 2.9900 · 10 -3 kg / m 2 s

1 pound / second · foot 2 (lb / sft 2 ) = 4.8824 kg / m 2 s

 

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Electric charge

International System Basic Unit (SI): coulomb or coulomb (C)

Definition : represents the amount of electric charge transported in one second by a current of one ampere of electric current intensity (1C = 1A · s).

It can also be expressed in terms of electrical capacity (Farad, F) and voltage (V), according to the relationship: 1C = 1 F · V.

Equivalences :

1 C = 0.0002777 A · h

1 A · h = 3600 C

 

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Electrical capacity

International System Basic Unit (SI): Faradio (F)

Definition : A farad is the capacity of a capacitor that when subjecting its armatures to an electrical potential difference of 1 volt (1 V) they are charged with an amount of electricity equal to one coulomb (1 C).

Equivalences :

 

 

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Electric resistance

International System Basic Unit (SI): Ohm (Ω)

Definition : An ohm is the electrical resistance that exists between two points of a conductor, when applying a constant potential difference of 1 volt causes a current of intensity of 1 ampere.

Equivalences :

 

 

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Electric conductivity

International System (SI) Basic Unit: Siemens per meter (S / m)

Definition : electrical conductivity represents the ability or ease of a material to let electric current pass and is inverse to resistivity. Its unit is the siemens per meter (S / m).

Values ​​of electrical conductivity :

  • Metals:

– Silver: 63.010 6 S / m

– Copper: 59.6 · 10 6 S / m

– Gold: 45.5 · 10 6 S / m

– Aluminum: 37.8 · 10 6 S / m

– Tungsten: 18.2 · 10 6 S / m

– Iron: 15.3 · 10 6 S / m

  • Semiconductors:

– Carbon: 2.80 · 10 4 S / m

– Germanium: 2.20 · 10 -2 S / m

– Silicon: 1.60 · 10 -5 S / m

  • Insulators:

– Glass: between 10 -10 and 10 -14 S / m

– Lucite: <10 -13 S / m

– Mica: between 10 -11 and 10 -15 S / m

– Teflon: <10 -13 S / m

– Paraffin: 3.37 · 10 -17 S / m

– Quartz: 1.3310 -18 S / m

  • Liquids:

– Sea water: 5 S / m

– Drinking water: between 0.0005 and 0.05 S / m

– Deionized water: 5.5 · 10 -6 S / m

 

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Thermal transmittance

Definition : Thermal transmittance ( U ) is the amount of energy that passes through, in the unit of time, the surface unit of a construction element with flat and parallel faces when there is a temperature difference of one degree between these faces. Thermal transmittance is the inverse of thermal resistance.

Mathematical expression :

U   = W
2 · K

 

 

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Luminous flux

International System Basic Unit (SI): lumen (lm)

Definition : The lumen is the unit derived from the International System of Units to measure the luminous flux. Luminous flux is the part of the total radiant power emitted by a light source that is capable of affecting the sense of sight, that is, to which the human eye is sensitive. The part of the radiation emitted by the radiating focus outside the visible spectrum does not contribute to the luminous flux.

Symbol : Φ

Equivalences :

1 lm = 1 cd · sr = 1 lx · m 2

 

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Illuminance

International System Basic Unit (SI): lux (lx)

Definition : illuminance is the amount of luminous flux that strikes a surface per unit area. The lux (lx) being the unit derived from the International System of Units for the measurement of illuminance or illumination level.
Equivalent 1 lux = 1 lm / m 2 .

Symbol : E

Equivalences :

E = Φ
S

 

where:

E is the illuminance, measured in lux.

Φ is the luminous flux, in lumen.

S is the differential element of emission area considered, in square meters.

 

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Luminance

International System (SI) Basic Unit: cd / m 2  or Nits

Definition : luminance is defined as the ratio of light intensity to the apparent surface seen by the eye in a certain direction. In photometry, luminance is defined as the angular and surface density of light flux that strikes, passes through, or emerges from a surface in a certain direction. Equivalent to 1 nit = 1 cd / m 2 .

Symbol : L

Equivalences :

L = I
apparent

 

where:

L is the luminance, measured in Nits or candela / meter 2 .

I is the light intensity, measured in candles.

Apparent S    is the differential element of apparent surface (S apparent = S · cosα), in square meters.

 

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Light performance or efficiency

International System Basic Unit (SI): lm / W (lumen / watt)

Definition : the luminous efficiency or performance of a light source is defined as the ratio between the emitted luminous flux and the power consumed by said source. It represents the useful power part of the total power consumed by the lamp. A higher performance, lower consumption of the lamp.

Symbol : η

Equivalences :

η = Φ
W

 

where:

η is the light output.

Φ is the luminous flux, in lumen.

W is the power consumed by the source, in watts.

 

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Frequency

International System Basic Unit (SI): hertz, hertz or hertz (Hz)

Definition : A hertz is the frequency of an oscillation that a particle undergoes in a period of time of one second. Thus, a phenomenon with a frequency of two hertz means that it repeats twice per second. In short, the number of hertz refers to the number of cycles that occur per second, that is, 100 Hz is 100 cycles per second, 1 kHz (1 kilohertz) is equal to 1000 cycles per second, 1 MHz (1 Megahertz) it’s 10 6 cycles per second, and so on.

1 Hz   = one
s

 

Symbol :   f

Equivalences :

f   = one
T

 

where   T   is the period or period of oscillation of the signal.

 

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Period

International System Basic Unit (SI): second (s)

Definition : the period of an oscillation or wave is the time elapsed between two equivalent points of the wave, that is, it is the time lapse that separates two instants in which the system is in exactly the same state. Thus, the period of oscillation of a wave is the time it takes to complete a wavelength, that is, the time it takes for one cycle of the wave to start again. Also, for example, the period is the time elapsed between two ridges or between two successive valleys of a wave movement. The period is the inverse of the frequency.

Symbol :   T

Equivalences :

T   = one
F

 

where   f   is the frequency of the signal.

 

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Irradiance

Basic Unit International System (SI): W / m 2

Definition : Irradiance is the incident power density on a surface, or the incident energy on a surface per unit time and unit area, of all types of electromagnetic radiation.

Symbol :   E

Equivalences :

E   = inc
s

 

where:

E    is irradiance.

inc    is the incident power of radiation, in watts.

s    is the area of ​​the surface on which the wave impinges, in square meters.

 

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Irradiation

International System (SI) Basic Unit: kWh / m 2

Definition : Irradiation is defined as the incident energy on a surface per unit area and over a certain period of time.

 

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Voltage or electrical potential difference

International System Basic Unit (SI): Volt ( V )

Definition : The volt is the unit derived from the International System to quantify the voltage or electric potential difference.

Volt ( V ) is defined as the potential difference across a conductor when a current of one ampere ( A ) uses one watt ( W ) of power to move, or else, the volt is defined as the potential difference existing between two points such that a work of 1 joule ( J ) has to be carried out to transfer from one point to another a charge of 1 coulomb ( C ).

Therefore, the electrical voltage, which represents the work per charge unit carried out by the electric field to move a charged particle between two determined positions, is independent of the path traveled by the charge and depends exclusively on the electrical potential of the starting and ending points. of the field.

Equivalences :

V   = J
C

 

V   = W
TO

 

V   = N · m
Ace

 

V   = N · m
C

 

V   = kg · m 2
A · s 3

 

 

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Moment of strength

International System Basic Unit (SI): Newton meter ( N · m )

Definition : The moment ( or ) a force F applied at a point P with respect to a point O is given by the vector product of the vector OP by the force vector F , that is, or = OP x F .

It is also called dynamic momentum or simply momentum , and is occasionally also called torque extracted from the English term ( torque ).

Equivalences :

1 N · m = 1.00 · 10 7 dyn · cm

1 Nm = 0.1019716 kgfm

1 Nm = 0.001 kNm

1 Nm = 0.1019716 kpm

1 Nm = 1000mNm (millinewton meter)

1 Nm = 11,80097 ozf · ft

1 Nm = 141.6116 ozf · in

1 Nm = 0.737561 lbf · ft

1 Nm = 8.85075 lbf · in

 

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Thermal conductivity

International System Basic Unit (SI): W / m · K

Definition : Thermal conductivity ( λ ) is the physical property that measures the ability of a material to conduct heat.

In this way, that a material has a thermal conductivity of 1 watt per meter and kelvin ( 1 W / m · K ), indicates that a quantity of heat of 1 July ( 1 J ) propagates through the material, in 1 second , by a surface of the material 1 m 2 , through a material thickness of 1 m , and when the temperature difference between the two faces of the material is of 1 K .

Symbol :   λ

Equivalences :

1 W / m · K = 1 J / s · m · K

 

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Thermal resistance

International System Basic Unit (SI): m 2 · K / W

Definition : Thermal resistance ( R ) represents the ability of a material to resist the flow of heat through it. In homogeneous materials it is the quotient between the thickness of the material and the thermal conductivity of the material; while in non-homogeneous materials the thermal resistance is equal to the inverse of its conductivity, obtained as a weighted average of the conductivity coefficients of each element that make it up.

Symbol :   R

Calculation :

  • Homogeneous materials:
R   = and
λ

 

being,

e     the thickness of the material layer, m

λ     the thermal conductivity of the material, W / (K · m)

  • Heterogeneous materials:
R   = one
C

 

being,

C     thermal conductance, W / (K · m 2 )

 

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Thermal Conductance

International System Basic Unit (SI): W / m 2 · K

Definition : Thermal conductance ( C ) is a measure of heat transfer through materials, which in turn can be made up of one or more layers.

In this case, thermal conductance measures the amount of heat transferred through the material, when the temperature difference between both sides of the material is one degree, at a unit time and surface, for a given thickness of material.

The thermal conductance ( C ) can be calculated either by dividing the thermal conductivity of the material by the layer thickness, or as the inverse of the unit thermal resistance.

Symbol :   C

Calculation :

C   = λ
and

 

being,

λ     the thermal conductivity of the material, W / (K · m)

e     the thickness of the material layer, m

C   = one
R

 

being,

R     the thermal resistance, 2 · K / W

 

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Specific heat

International System Basic Unit (SI): J / kg · K

Definition : Specific heat ( c ), also called specific heat capacity, is defined as the amount of heat that must be supplied to the unit of mass to raise its temperature by one degree (Kelvin or degree Celsius). The value of the specific heat depends on the initial temperature.

The specific heat depends, in addition to the temperature, on the pressure. It is an intensive property, representative of each matter, and independent of the amount of matter in the body or system being considered. Specific heat represents the ability of a body or substance to store heat, that is, the higher the specific heat of a substance, the more heat energy is needed to increase its temperature.

For example, the specific heat of water is  4180 J / kg · K   ( 1 cal / g · K ) in the temperature range of 14.5 ° C to 15.5 ° C and at atmospheric pressure.

Symbol :   c

Calculation :

c   = C
m

 

where,

c     is the specific heat, J / kg · K

C     is the heat capacity, J / K

m     is the mass of the substance, kg

 

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Heat capacity

International System Basic Unit (SI): J / K

Definition : The heat capacity ( C ) is defined as the energy required to increase the temperature of a given substance by one degree (Kelvin or degree Celsius).

Heat capacity depends on temperature and pressure, and is an extensive property, that is, it also depends on the amount of matter in the body or system being considered.

Symbol :   C

Calculation :

C = c · m

where,

C     is the heat capacity, J / K

c     is the specific heat, J / kg · K

m     is the amount of mass of the substance, kg

 

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Magnetic induction

Basic Unit International System (SI): Tesla (T)

Definition : Magnetic induction, or magnetic flux density ( B ), is the magnetic flux that causes a moving diffusion charge for each unit of area normal to the direction of flux. It is also called a magnetic field strength.

Symbol :   B

The unit of the magnetic flux density in the International System of Units is the tesla (T).

The tesla (symbol T ) is the magnetic induction unit (or magnetic flux density) of the International System of Units (SI). It is defined as a uniform magnetic induction that, normally distributed over a surface of one square meter, produces through this surface a total magnetic flux of a weber.

Equivalences :

1 T = 1 Wb · m -2 = 1 kg · s -2 · A -1 = 1 kg · C -1 · s -1

A Tesla is also defined as the induction of a magnetic field that exerts a force of 1 N (newton) on a charge of 1 C (coulomb) that moves at a speed of 1 m / s within the field and perpendicular to the lines of magnetic induction.

1 T = 1 N · s · m -1 · C -1

Basic Unit in the Cegesimal System of Units (CGS):   Gauss (G)

A gauss (G) is a unit of magnetic field of the Cegesimal System of Units (CGS). A gauss (G) is defined as a maxwell per square centimeter.

1 gauss = 1 maxwell / cm 2

A gauss is equivalent to 10 -4 tesla:

1T = 10,000G

 

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Magnetic flux

International System Basic Unit (SI): Weber (Wb)

Definition : Magnetic flux ( Φ ) is a measure of the amount of magnetism. It is calculated from the magnetic field, the surface on which it acts and the angle of incidence formed between the lines of the magnetic field and the different elements of said surface.

Symbol :   Φ

The unit of magnetic flux in the International System of Units is the weber (Wb).

The weber (symbol Wb ), is the unit of the magnetic flux or magnetic induction flux of the International System of Units (SI). It is defined as the magnetic flux that, when passing through a circuit with a single turn, produces an electromotive force of 1 volt in it if said flux is canceled in 1 second by uniform decrease.

Equivalences :

1 Wb = 1 V · s = 1 T · m 2 = 1 m 2 · kg · s -2 · A -1

Basic Unit in the Cegesimal System of Units (CGS):   Maxwell (Mx)

A maxwell (Mx), in a magnetic field of a measuring gauss, is the total flow around the surface in an area of ​​one square centimeter perpendicular to the field.

1 maxwell = 1 gauss · cm 2

A maxwell (Mx) is equivalent to 10 -8 weber (Wb):

1 Wb = 10 8 Mx

 

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Magnetic Permeability

International System Basic Unit (SI): T · m / A = Wb / A · m = H / m

UNITS: m = meter; A = amp; T = tesla; Wb = weber; H = Henry

Definition : Magnetic permeability ( µ ) is the ability of a substance or medium to attract and pass magnetic fields through it. Magnetic permeability is a measure of how easily a substance or medium passes through the magnetic field, that is, whether it is a good conductor of the magnetic field or not.

Symbol :   µ

Permeability is a magnetic characteristic of each matter. The pemeabilidad in vacuum ( μ or ) is low, while in other materials such as iron is high.

Magnetic permeability of a material,   µ = P r · µ o

where:

r = relative permeability

µ 0 = vacuum permeability = 4π · 10 -7 (T · m / A = Wb / A · m = H / m)

The magnetic permeability of AIR and VACUUM is approximately the same.

Diamagnetic materials are those that have values ​​for Pr that are slightly less than unity (for example, solid lead: 0.999 984).

Paramagnetic materials are those with values ​​for Pr that are slightly greater than unity (for example, for solid aluminum: 1,000 021).

Ferro-magnetic materials , such as iron and its alloys, which have Pr values of around 5000 or even higher.

Material – Relative permeability ( Pr )

air: 1.00

aluminum: 1.000023

copper: 0.99999

gold: 0.999964

lead: 0.999983

silver: 0.999974

soft iron: 5000

permalloy: 80000

 

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Table of multiples and submultiples

TABLE OF MULTIPLE AND SUBMULTIPLE

 

 

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English system of units of measurement

ENGLISH UNITS SYSTEM

The English System of Units , or also called the Imperial System of Units, is the set of non-metric units of measurement that are currently used in the United Kingdom and in many other English-speaking territories (such as the United States of America).

  • Length Units:

The system for measuring lengths in the English System is based on the inch, the foot, the yard and the mile.

1 inch (inch, in) = 0.0254m = 25.4mm

1 foot (foot, ft) = 12 in = 0.3048 m = 30.48 cm

1 yard (yard, yd) = 3 ft = 36 in = 0.9144 m = 91.44 cm

1 rod (rd) = 1 perch = 5.5 and d = 16.5 ft = 198 in = 5.0292 m

1 mile (mile, mi) = 1760 yd = 1609.34 m

1 league = 5280 and d = 4828.03 m

1 furlong (fur) = 40 rd = 110 and d = 660 ft = 201,168 m

1 Mile = 8 fur = 5280 ft = 1.609347 km (agriculture)

To measure depths of the sea, the fathoms (breaststroke) are used:

1 breaststroke = 6 ft = 72 in = 1.83 m

  • Surface Units:

The system for measuring surfaces in the English System is based on the square inch (sq in, in 2 ).

1 in 2 (sq in) = 6.451610 -4 m 2 = 645.16 mm 2

1 ft 2 (sq ft) = 144 sq in = 9.290310 -2 m 2 = 929.03 cm 2

1 rod 2 (sq rd) = 272.25 sq ft = 25,316 m 2

1 yd 2 (sq yd) = 8.361310 -1 m 2

1 acre = 4 roods = 160 sq rd = 4840 sq yd = 43560 sq ft = 4046.9 m 2

1 mile 2 (sq mi) = 640 acres = 2.59 km 2 = 2.590010 6 m 2

  • Volume Units:

The cubic inch (cu in), the cubic foot (cu ft), and the cubic yard (cu yd) are commonly used to measure volume in the English System of Measurements. But there is also a group of specific units to measure volumes of dry materials, as shown below.

1 in 3 (cu in) = 1.638710 -5 m 3 = 16.387065 cm 3

1 ft 3 (cu ft) = 1728 cubic inches (cu in) = 2.831710 -2 m 3 = 28,317 L

1 yd 3 (cu yd) = 27 cubic feet (cu ft) = 7.646 hL = 7.6455 · 10 -1 m 3

1 US gal = 3.785310 -3 m 3

1 UK gal = 4.546010 -3 m 3

1 barrel (petroleum US) = 1.589810 -1 m 3

1 lube oil barrel = 2.081910 -1 m 3

1 bucket = 2.3659 · 10 -4 m 3

1 gill = 1.182910 -4 m 3

1 register ton = 100 ft 3 = 2.8317 m 3

1c = 8 UK bushels = 32 pecks = 64 Uk gallons = 256 quarts = 512 pints = 0.2909 m 3

Specific units to measure volumes of dry materials stored in bulk (United States of America):

1 Pint (pt) = 550,610 mL

1 Quarter (qt) = 2 pints = 1,101 L

1 Gallon (gal) = 4 quarts = 4,404 L

1 Peck (pk) = 8 quarts = 2 gallons = 8.809 L

1 US Bushel (bu) = 2150.42 cubic inches = 4 pk = 3.523910 -2 m 3 = 35,239 L

 

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Values ​​of the Universal Physical Constants

PHYSICAL CONSTANTS

Elemental charge of the electron ( e ) = -1.602176 · 10 -19  C

Resting mass of the electron ( e ) = 9.109110 -31  kg

Elemental charge of the proton ( p ) = 1.602176 · 10 -19  C

Resting mass of the proton ( p ) = 1.672510 -27  kg

Neutron resting mass ( e ) = 1,67910 -27  kg

Planck constant ( h ) = 6,626 · 10 -34  J · s = 6,626 · 10 -27  erg · s

Rydberg constant of infinity (  ) = 1,097373156810 7  m -1

Rydberg constant for hydrogen ( H ) = 10,967,758,341 m -1

Coulomb constant in vacuum ( k ) = 9 · 10 9  N · m 2 / C 2

Dielectric or vacuum permittivity constant ( ε 0 ) = 8.85 · 10 -12  C 2 / N · m 2  = 8.85 · 10 -12  F / m

Faraday constant ( k ) = 96,485.33 C / mol

Boltzmann constant ( k ) = 1,3806 · 10 -23  J / K = 1,3806 · 10 -16  erg / K

Stefan-Boltzmann constant ( σ ) = 5.6704 · 10 -8  W / m 2 · K 4

Permeability constant = 1.26 · 10 -6  H / m

Universal gravitational constant ( G ) = 6.67384 · 10 -11  N · m 2 · kg -2

Universal gas constant ( R ) = 8.314472 J · mol -1 · K -1  = 0.08205746 atm · L · mol -1 · K -1  = 1.987207 cal · mol -1 · K -1

Vacuum magnetic permeability ( μ 0 ) = 4π · 10 -7  N · A -2  = 1.2566 · 10 -6  H / m = 4π · 10 -7  T · m

Bohr magnet ( μ B ) = 9,274 · 10 -24  J / T = 9,274 · 10 -21  erg / G = 5,788 · 10 -5  eV / T

Electronvolt ( eV ) = 1.6021810 -19  J

Atomic mass unit ( u ) = 1.660510 -27  kg

Avogadro’s number ( L, N A ) = 6,02210 23  mol -1

Molar volume ( m ) = 22.4 L

Triple point of water ( π ) = 273.16 K (at a partial pressure of water vapor of 0.61 kPa)

Speed ​​of light in vacuum ( c ) = 299,792,458 m / s

Average radius of the Earth ( mT ) = 6.371 km

Distance from Earth to the Moon ( T-L ) = 384,400 km

Distance from Earth to the Sun ( T-S ) = 149.6 · 10 6  km

Earth Mass ( T ) = 5.97610 24  kg

Moon mass ( L ) = 7.36 · 10 22  kg

Acceleration of gravity on Earth ( g ) = 9.80665 m · s -2  (9.81 m · s -2 )

Acceleration of gravity on the Moon ( L ) = 1.62 m · s -2

Fine structure constant ( α ) =  2 / ( h · c · 4 · π · ε 0 ) = 1 / 137,03599911

 

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