Table 7.6 — EUs whose label begins with M-Z

Label Symbol Quantity Concept definition EQ label Code Reference Supplemental references
METRE m (instantaneous) sound particle displacement Instantaneous displacement of a particle in a medium from what would be its position in the absence of sound waves. LENGTH 142 ISO 31-7:1992, 7-10.a  
Bohr radius The radius of the electron orbit having the lowest energy in the Bohr atom; 0,5292 x 10-10 m. ISO 31-9:1992, 9-8.a  
Burgers vector The vector characterizing a dislocation, i.e. the closing vector in a Burgers circuit encircling a dislocation line. ISO 31-13:1992, 13-7.a  
coherence length The distance in a superconductor over which the effect of a perturbation is appreciable. ISO 31-13:1992, 13-39.a  
Compton wavelength The wavelength associated with the mass of any particle. ISO 31-9:1992, 9-27.a  
diffusion length The mean distance that a particle travels before it is absorbed or recombines. ISO 31-13:1992, 13-34.a  
diffusion length The square root of the diffusion area. ISO 31-10:1992, 10-41.a  
electron radius The classical theoretical radius of an electron, 2,82 x 10-15 m, obtained by equating the rest mass energy of an electron to the coulomb energy. ISO 31-9:1992, 9-26.a  
focal distance For a single thin lens, the distance from the centre of the lens to the focal point. ISO 31-6:1992, 6-45.a  
fundamental lattice vector The fundamental translation vectors for the crystal lattice. ISO 31-13:1992, 13-1.a  
half-thickness (half-value thickness) The thickness of the attenuating layer that reduces the current density of a unidirectional beam to one-half of its initial value. ISO 31-10:1992, 10-17.a  
lattice plane spacing The distance between successive lattice planes. ISO 31-13:1992, 13-3.a  
lattice vector The translation vector which maps the crystal lattice on itself. ISO 31-13:1992, 13-1.a  
length The length of the path travelled by light in vacuum during a time interval of 1 / 299 792 458 of a second.
SI base unit.		 ISO 31-0:1992, Table 1 ISO 31-1:1992, 1-3.a
mean free path For a molecule, the average distance between two successive collisions. ISO 31-8:1992, 8-38.a  
mean free path The average distance that particles travel between two successive specified reactions or processes. ISO 31-10:1992, 10-39.a  
mean free path The average distance travelled by a particle between collisions with another particle in the system. ISO 31-13:1992, 13-16.a  
mean linear range The distance that a particle penetrates in a given substance under specified conditions averaged over a group of particles having the same initial energy. ISO 31-10:1992, 10-21.a  
migration length The square root of the migration area. ISO 31-10:1992, 10-41.a  
nuclear radius The average radius of the volume in which the nuclear matter is included. ISO 31-9:1992, 9-17.a  
slowing-down length The square root of the slowing-down area. ISO 31-10:1992, 10-41.a  
wavelength The distance in the direction of propagation of a periodic wave between two successive points where at a given time the phase is the same. ISO 31-6:1992, 6-3.a ISO 31-2:1992, 2-5.a; ISO 31-7:1992, 7-5.a
METRE_FOURTH_POWER m4 second moment of area (second axial moment of area) The second axial moment of area of a plane area (section) about an axis in its plane is the sum (integral) of the products of its elements of area and the squares of their distances from the axis or point. SECOND_MOMENT_AREA 143 ISO 31-3:1992, 3-20.a  
METRE_KELVIN m · K second radiation constant The constant c2 in the expression for the spectral concentration of the radiant exitance of a full radiator (black body). SECOND_RADIATION-
_CONSTANT		 144 ISO 31-6:1992, 6-20.a  
METRE_PER_HOUR m/h velocity The distance divided by time.
1 m/h = 1 / 3,6 x 10-3 m/s (exactly).		 SPEED 145 ISO 31-1:1992, 1-10.a ISO 31-0:1992, 2.3.2.3
METRE_PER_SEC m/s group velocity The velocity of a packet of waves having different frequencies and phase velocities. SPEED 146 ISO 31-2:1992, 2-8.a  
neutron speed The magnitude of the neutron velocity. ISO 31-10:1992, 10-30.a  
phase velocity In wave propagation, the velocity of a surface of constant phase; this would be the speed of the wave. ISO 31-2:1992, 2-8.a  
velocity The distance divided by time. ISO 31-1:1992, 1-10.a  
METRE_PER_SEC_SQD m/s2 acceleration The change in velocity divided by time. ACCELERATION 147 ISO 31-1:1992, 1-11.a ISO 31-7:1992, 7-12.a
MINUTE min time 1 min = 60 s (exactly). TIME 150 ISO 31-0:1992, Table 4 ISO 31-1:1992, 1-7.b
MINUTE_ARC ' plane angle The angle between two half-lines terminating at the same point is defined as the ratio of the length of the included arc of the circle (with its centre at that point) to the radius of that circle.
1' = (1 / 60)º = (π / 10 800) rad (exactly).		 PLANE_ANGLE 151 ISO 31-0:1992, Table 4 ISO 31-1:1992, 1-1.c
MINUTE_PER_CUBIC_METRE min/m3 volumetric entity dose (any elementary entity: atoms, molecules, ions, electrons, other particles, or specified groups of such particles) The time integral of exposure to a number of molecules or particles divided by their volume.
1 min/3 = 60 s/m3 (exactly).		 VOLUMIC_DOSE 152 ISO 31-8:1992, 8-10.a ISO 31-0:1992, 2.3.2.2 (derived)
MOLE mol amount of substance The amount of substance in 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.
SI base unit.		 AMOUNT_SUBSTANCE 153 ISO 31-0:1992, Table 1 ISO 31-8:1992, 8-3.a
MOLE_PER_CUBIC_M mol/m3 concentration (amount-of-substance concentration) The amount of substance divided by the volume of the mixture. CONCENTRATION 154 ISO 31-8:1992, 8-13.a  
MOLE_PER_KG mol/kg ionic strength The mass concentration of ions in a solution. MOLALITY_SOLUTE 155 ISO 31-8:1992, 8-46.a  
molality of solute The amount of substance of solute in a solution divided by the mass of the solvent. ISO 31-8:1992, 8-16.a  
MOLE_PER_LITRE mol/l, mol/L concentration (amount-of-substance concentration) The amount of substance divided by the volume of the mixture.
1 mol/l = 103 mol/m3 (exactly).		 CONCENTRATION 156 ISO 31-8:1992, 8-13.b  
MOLE_PER_MOLE mol/mol mole fraction (of B) The ratio of the amount of substance of B to the amount of substance of the mixture.
1 mol/mol = 1.		 MOLE_FRACTION 157 ISO 31-8:1992, 8-14.a ISO 31-0:1992, 2.3.3
NEPER Np field quantity ratio (level difference) Twice the natural logarithm of a field quantity ratio.
1 Np is the level of a field quantity when ln (F/F0) = 1 where F and F0 represent two amplitudes of the same kind, F0 being a reference amplitude.		 FIELD_OR_POWER-
_LEVEL_DIFF		 159 ISO 31-2:1992, 2-9.a  
logarithmic decrement The product of damping coefficient and period. ISO 31-7:1992, 7-25.a ISO 31-2:1992, 2-12.a
power quantity ratio (level difference) The natural logarithm of a power quantity ratio.
1 Np is the level of a power quantity when 1/2 ln (P/P0) = 1 where P and P0 represent two powers of the same kind, P0 being a reference power.		 ISO 31-2:1992, 2-10.a  
NEPER_PER_SECOND Np/s damping coefficient The factor defining the rate of exponential amplitude decay in a periodic or acoustic system. DAMPING_COEFFICIENT 160 ISO 31-7:1992, 7-23.b ISO 31-2:1992, 2-11.b
NEWTON N force An external agent that causes a change in the motion of a free body, or that causes stress in a fixed body; proportional to the rate of change in momentum.
1 N = 1 (m · kg)/s2.		 FORCE 161 ISO 31-0:1992, Table 2 ISO 31-3:1992, 3-9.a
NEWTON_M_SQD_PER_KG_SQD (N · m2)/kg2 gravitational force between two particles The force of attraction between massive bodies due to gravitation.
1 N · m2/kg2 = 1 m3/(kg · s2).		 GRAVITATIONAL_FORCE 162 ISO 31-3:1992, 3-14.a  
NEWTON_METRE N · m moment of force Torque, the tendency of a force to cause an object to rotate about a given point.
1 N · m = 1 (m2 · kg2)/s2.		 MOMENT_FORCE 163 ISO 31-3:1992, 3-12.a  
NEWTON_METRE_SECOND N · m · s angular impulse The integral over time of all torques applied.
1 N · m · s = 1 (m2 · kg2)/s.		 ANGULAR_IMPULSE 164 ISO 31-3:1992, 3-13.a  
NEWTON_PER_METRE N/m surface tension The stretching force required to form a liquid film, tending to minimize the area of a surface; equal to the surface energy of the liquid per unit length of the film at equilibrium.
1 N/m = 1 kg/s2.		 SURFACE_TENSION 165 ISO 31-3:1992, 3-25.a  
NEWTON_PER_SQ_M N/m2 fugacity (in a gaseous mixture) A function substituting for pressure, allowing a real gas system to be considered by the same equations that apply to an ideal gas. PRESSURE 166 ISO 31-8:1992, 8-20.a  
instantaneous sound pressure The difference between the instantaneous total pressure and the static pressure. ISO 31-7:1992, 7-9.a  
modulus of elasticity The stress per unit elastic strain, expressed as a ratio between the stress placed on a material and the strain, or dimensional response to stress. ISO 31-3:1992, 3-18.a  
osmotic pressure The excess pressure required to maintain osmotic equilibrium between a solution and the pure solvent separated by a membrane permeable only to the solvent. ISO 31-8:1992, 8-26.a  
partial pressure (of B, in a gaseous mixture) For a gaseous mixture, pB = xB·p, where p is the pressure. ISO 31-8:1992, 8-19.a  
pressure The force divided by the area over which it is applied. ISO 31-3:1992, 3-15.a  
pressure The force that is exerted per unit area.
1 N/m2 = 1 Pa = 1 kg/(m · s2).		 ISO 31-0:1992, Table 2  
static pressure The pressure that would exist in the absence of sound waves. ISO 31-7:1992, 7-9.a  
NEWTON_SECOND N · s impulse A vector quantity given by the integral over time of the force acting on a body, usually in a collision in which the time interval is very brief; it is equal to the change in the momentum of the body.
1 N · s = 1 (m · kg)/s.		 IMPULSE 167 ISO 31-3:1992, 3-10.a  
NEWTON_SECOND_PER_METRE (N · s)/m mechanical impedance At a surface (or at a point), the complex representation of total force divided by the complex representation of average particle velocity at that surface (or of particle velocity at that point) in the direction of the force.
1 (N · s)/m = 1 kg/s.		 MECHANICAL_IMPEDANCE 168 ISO 31-7:1992, 7-19.a  
OCTAVE none frequency interval The numerical value of a frequency interval in octaves is given by lb (f2/f1), when f2 is greater than f1. FREQUENCY_INTERVAL 169 ISO 31-7:1992, 7-3.a  
OHM Ω electrical resistance The electric potential difference divided by current when there is no electromotive force in the conductor.
1 Ω = 1 V/A = 1 (m2 · kg)/(s3 · A2).		 RESISTANCE 170 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-33.a; ISO 31-5:1992, 5-44.a
OHM_METRE Ω · m residual resistivity For metals, the resistivity extrapolated to zero thermodynamic temperature. RESISTIVITY 171 ISO 31-13:1992, 13-18.a  
resistivity The inherent ability of a material to resist current flow.
1 Ω · m = 1 (m3 · kg)/(s3 · A2).		 ISO 31-5:1992, 5-36.a  
PASCAL Pa fugacity (in a gaseous mixture) A function substituting for pressure, allowing a real gas system to be considered by the same equations that apply to an ideal gas. PRESSURE 173 ISO 31-8:1992, 8-20.a  
instantaneous sound pressure Difference between the instantaneous total pressure and the static pressure. ISO 31-7:1992, 7-9.a  
modulus of elasticity The stress per unit elastic strain, expressed as a ratio between the stress placed on a material and the strain, or dimensional response to stress. ISO 31-7:1992, 7-9.a  
osmotic pressure The excess pressure required to maintain osmotic equilibrium between a solution and the pure solvent separated by a membrane permeable only to the solvent. ISO 31-8:1992, 8-26.a  
partial pressure (of B, in a gaseous mixture) For a gaseous mixture, pB = xB·p, where p is the pressure. ISO 31-8:1992, 8-19.a  
pressure The force that is exerted per unit area.
1 Pa = 1 N/m2 = 1 kg/(m · s2).		 ISO 31-0:1992, Table 2 ISO 31-3:1992, 3-15.a
pressure The force divided by the area over which it is applied. ISO 31-3:1992, 3-18.a  
static pressure The pressure that would exist in the absence of sound waves. ISO 31-7:1992, 7-9.a  
PASCAL_PER_KELVIN Pa/K pressure coefficient The fractional change in the pressure of a gas sample divided by the fractional change in the temperature under specified conditions, such as constant volume.
1 Pa/K = 1 kg/(m · s2 · K).		 PRESSURE_COEFFICIENT 174 ISO 31-4:1992, 4-4.a  
PASCAL_PER_SEC Pa/s pressure change rate The rate of change in force is exerted per unit area.
1 Pa/s = 1 kg/(m · s3).		 PRESSURE_CHANGE_RATE 175 ISO 31-0:1992, 2.3.2.2 (derived)  
PASCAL_SEC Pa · s dynamic viscosity The constant of proportionality of the rate of deformation of a Newtonian fluid, directly proportional to the applied shear stress.
1 Pa · s = 1 kg/(m · s).		 DYNAMIC_VISCOSITY 176 ISO 31-3:1992, 3-23.a  
PASCAL_SEC_PER_CUBIC_METRE (Pa · s)/m3 acoustic impedance At a surface, the complex representation of sound pressure divided by the complex representation of volume flow rate.
1 (Pa · s)/m3 = 1 kg/(m4 · s).		 ACOUSTIC_IMPEDANCE 177 ISO 31-7:1992, 7-18.a  
PASCAL_SEC_PER_METRE (Pa · s)/m characteristic impedance of a medium At a point in a medium and for a plane progressive wave, the complex representation of sound pressure divided by the complex representation of particle velocity.
1 (Pa · s)/m = 1 kg/(m2 · s).		 SURFACE_DENSITY-
_MECH_IMPED		 178 ISO 31-7:1992, 7-20.a  
PHON none loudness level 1 phon is the loudness level when 2 lb (peff/p0)1 kHz = 0,1, where peff is the root-mean-square value of the sound pressure of a pure tone of 1 kHz, which is judged by a normal observer under standardized listening conditions as being as loud as the sound under investigation, and where p0 = 20 μPa. LOUDNESS_LEVEL 180 ISO 31-7:1992, 7-31.a  
RADIAN rad angle of optical rotation Angle through which plane-polarized light is rotated clockwise, as seen when facing the light source, in passing through an optically active medium. PLANE_ANGLE 186 ISO 31-8:1992, 8-51.a  
phase difference The relative angular displacement between a periodic quantity and a reference angle or between two sinusoidally varying quantities of identical frequencies. ISO 31-5:1992, 5-43.a  
plane angle The angle between two half-lines terminating at the same point is defined as the ratio of the length of the included arc of the circle (with its centre at that point) to the radius of that circle.
1 rad = 1 m/m = 1
A complete angle (full circle) is 2π rad.		 ISO 31-0:1992, Table 2 ISO 31-1:1992, 1-1.a
RADIAN_PER_METRE rad/m angular repetency (angular wave number) The reciprocal of the wavelength or the number of waves per unit angle along the direction of propagation. ANGULAR_REPETENCY 187 ISO 31-2:1992, 2-7.a ISO 31-6:1992, 6-5.a; ISO 31-7:1992, 7-7.a; ISO 31-13:1992, 13-10.a
RADIAN_PER_SEC rad/s angular frequency The number of cycles or revolutions divided by time. ANGULAR_VELOCITY 188 ISO 31-6:1992, 6-2.a ISO 31-9:1992, 9-14.a; ISO 31-9:1992, 9-15.a; ISO 31-13:1992, 13-11.a
angular frequency The frequency of rotation or vibration. ISO 31-2:1992, 2-4.a ISO 31-5:1992, 5-42.a; ISO 31-7:1992, 7-4.a
angular velocity The change in angular position divided by time. ISO 31-1:1992, 1-8.a  
pulsatance The angular velocity of a periodic quantity. ISO 31-2:1992, 2-4.a ISO 31-5:1992, 5-42.a; ISO 31-7:1992, 7-4.a
RADIAN_PER_SEC_SQD rad/s2 angular acceleration The change in angular velocity divided by time. ANGULAR_ACCELERATION 189 ISO 31-1:1992, 1-9.a  
SECOND s carrier life time The time constant for recombination or trapping of minority charge carriers in semiconductors. TIME 192 ISO 31-13:1992, 13-33.a  
half-life The average time required for the decay of one half of the atoms of a sample of a radioactive nuclide. ISO 31-9:1992, 9-37.a  
mean life The average amount of time an unstable radioisotope exists before it decays, equal to the reciprocal of the decay constant. ISO 31-9:1992, 9-31.a  
period (periodic time) The time of one cycle. ISO 31-2:1992, 2-1.a ISO 31-7:1992, 7-1.a
reactor time constant The time required for the neutron fluence rate in a reactor to change by the factor e when the fluence rate is rising or falling exponentially. ISO 31-10:1992, 10-48.a  
relaxation time The time constant for exponential decay towards equilibrium. ISO 31-13:1992, 13-33.a  
reverberation time The time required for the average sound energy density in an enclosure to decrease to 10-6 of its initial value (i.e., by 60 dB) after the source has stopped. ISO 31-7:1992, 7-30.a  
time 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 caesium-133 atom.
SI base unit.		 ISO 31-0:1992, Table 1 ISO 31-1:1992, 1-7.a
time constant (relaxation time) The reciprocal of the damping coefficient. ISO 31-7:1992, 7-24.a  
time constant of an exponentially varying quantity The time after which the quantity would reach its limit if it maintained its initial rate of variation. ISO 31-2:1992, 2-2.a  
SECOND_ARC " plane angle The angle between two half-lines terminating at the same point is defined as the ratio of the length of the included arc of the circle (with its centre at that point) to the radius of that circle.
1" = (1 / 3 600)º = (π / 648 000) rad (exactly).		 PLANE_ANGLE 193 ISO 31-0:1992, Table 4 ISO 31-1:1992, 1-1.d
SECOND_PER_CUBIC_M_RADIAN s/(m3 · rad) spectral concentration of vibrational modes (in terms of angular frequency) The number of vibrational modes in an infinitesimal interval of angular frequency, divided by the size of that interval and by volume.
1 s/(m3 · rad) = 1 s/m3 (exactly).		 SPECTRAL_CONC-
_VIBRAT_MODES		 194 ISO 31-13:1992, 13-13.a  
SECOND_PER_CUBIC_METRE s/m3 volumetric entity dose (any elementary entity: atoms, molecules, ions, electrons, other particles, or specified groups of such particles) The time integral of exposure to a number of molecules or particles divided by their volume. VOLUMIC_DOSE 195 ISO 31-8:1992, 8-10.a ISO 31-0:1992, 2.3.2.2 (derived)
SIEMENS S admittance The reciprocal of the complex representation of potential difference divided by the complex representation of current; the reciprocal of impedance. ELECTRIC_CONDUCTANCE 196 ISO 31-5:1992, 5-45.a  
electrical conductance The electric current divided by potential difference when there is no electromotive force in the conductor; the reciprocal of electrical resistance.
1 S = 1 Ω-1 = 1 (s3 · A2)/(m2 · kg).		 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-34.a
SIEMENS_M_SQD_PER_MOLE (S · m2)/mol molar conductivity The conductivity divided by the amount-of-substance concentration.
1 (S · m2)/mol = 1 (s3 · A2)/(kg · mol).		 MOLAR_CONDUCTIVITY 197 ISO 31-8:1992, 8-49.a  
SIEMENS_PER_METRE S/m electrical conductivity The electric current density divided by the electric field strength.
1 S/m = 1 (s3 · A2)/(m3 · kg).		 ELECTRIC-
_CONDUCTIVITY		 198 ISO 31-5:1992, 5-37.a  
electrolytic conductivity The electrolytic current density divided by the electric field strength. ISO 31-8:1992, 8-48.a  
SIEVERT Sv dose equivalent of ionizing radiation The product of D, Q and N, at the point of interest in tissue, where D is the absorbed dose, Q is the quality factor and N is the product of any other modifying factors.
1 Sv = 1 J/kg = 1 m2/s2.		 DOSE_EQUIVALENT 199 ISO 31-0:1992, Table 3 ISO 31-10:1992, 10-52.a
SONE none loudness A normal observer's auditory estimate of the ratio between the strength of the sound considered and that of a reference sound having a loudness level of 40 phons. LOUDNESS 200 ISO 31-7:1992, 7-32.a  
SQ_METRE m2 area The product of length and width. AREA 201 ISO 31-1:1992, 1-5.a ISO 31-7:1992, 7-29.a; ISO 31-9:1992, 9-16.a; ISO 31-10:1992, 10-3.a; ISO 31-10:1992, 10-16.a; ISO 31-10:1992, 10-40.a
SQ_METRE_AMP_PER_JOULE_SEC (m2 · A)/(J · s) gyromagnetic coefficient (gyromagnetic ratio) The ratio of the magnetic moment to the intrinsic angular momentum of a spinning particle.
1 (m2 · A)/(J · s) = 1 (s · A)/kg.		 GYROMAGNETIC-
_COEFFICIENT		 202 ISO 31-9:1992, 9-12.a  
SQ_METRE_AMPERE m2 · A magnetic moment (electromagnetic moment) A vector quantity, the vector product of which with the magnetic flux density of a homogeneous field is equal to the torque. MAGNETIC_MOMENT 203 ISO 31-5:1992, 5-27.a  
magnetic moment of particle or nucleus Expectation value of the component of the electromagnetic moment in the direction of the magnetic field in the quantum state with maximum magnetic quantum number. ISO 31-9:1992, 9-11.a  
SQ_METRE_KELVIN_PER_WATT (m2 · K)/W thermal insulance (coefficient of thermal insulation) The temperature difference divided by areic heat flow rate.
1 (m2 · K)/W = 1 (s3 · K)/kg.		 THERMAL_INSULANCE 204 ISO 31-4:1992, 4-11.a  
SQ_METRE_PER_JOULE m2/J spectral cross-section Cross-section for a process in which the energy of the ejected or scattered particle is in an element of energy, divided by this element.
1 m2/J = 1 s2/kg.		 SPECTRAL_CROSS-
_SECTION		 205 ISO 31-10:1992, 10-5.a  
SQ_METRE_PER_JOULE_SR m2/(J · sr) spectral angular cross-section Cross-section for ejecting or scattering a particle into an element of solid angle with energy in an element of energy, divided by the product of these two elements.
1 m2/(J · sr) = 1 s2/(kg · sr).		 SPECTRAL_ANGULAR-
_CROSS_SECT		 206 ISO 31-10:1992, 10-6.a  
SQ_METRE_PER_KG m2/kg mass attenuation coefficient The linear attenuation coefficient divided by the volumic mass of the substance. MASS_ATTENUATION-
_COEFF		 207 ISO 31-10:1992, 10-14.a  
SQ_METRE_PER_MOLE m2/mol molar absorption coefficient The linear attenuation coefficient divided by the volumic amount of the substance. MOLAR_ABSORPTION-
_COEFF		 208 ISO 31-6:1992, 6-43.a  
molar attenuation coefficient The linear attenuation coefficient divided by the amount-of-substance concentration. ISO 31-10:1992, 10-15.a  
SQ_METRE_PER_SECOND m2/s diffusion coefficient The rate at which atoms or ions diffuse across a surface area per unit time. KINEMATIC_VISCOSITY 209 ISO 31-8:1992, 8-39.a ISO 31-10:1992, 10-32.a
kinematic viscosity The absolute viscosity of a fluid divided by its density. ISO 31-3:1992, 3-24.a  
thermal diffusivity The ratio of thermal conductivity to the heat capacity per unit volume for a material. ISO 31-4:1992, 4-14.a  
SQ_METRE_PER_STERADIAN m2/sr angular cross-section The cross-section for ejecting or scattering a particle into an element of solid angle, divided by this element. ANGULAR_CROSS-
_SECTION		 210 ISO 31-10:1992, 10-4.a  
SQ_METRE_PER_VOLT_SECOND m2/(V · s) mobility The average drift velocity imparted to a charged particle in a medium by an electric field, divided by the field strength.
1 m2/(V · s) = 1 (s2 · A)/kg.		 MOBILITY 211 ISO 31-10:1992, 10-26.a  
SQ_METRE_RADIAN_PER_KG (m2 · rad)/kg massic optical rotatory power (specific optical rotatory power) The cross-sectional area of a linearly polarized light beam times its angle of optical rotation, divided by the mass of the optically active component in the path. MASSIC_OPTICAL_ROT-
_POWER		 212 ISO 31-8:1992, 8-53.a  
SQ_METRE_RADIAN_PER_MOLE (m2 · rad)/mol molar optical rotatory power The cross-sectional area of a linearly polarized light beam times its angle of optical rotation, divided by the amount of substance of the optically active component in the path. MOLAR_OPTICAL_ROT-
_POWER		 213 ISO 31-8:1992, 8-52.a  
STERADIAN sr solid angle The solid angle of a cone is defined as the ratio of the area cut out on a spherical surface (with its centre at the apex of that cone) to the square of the radius of the sphere.
1 sr = 1 m2/m2 = 1
A complete angle over all space (full sphere) is 4π sr.		 SOLID_ANGLE 214 ISO 31-0:1992, Table 2 ISO 31-1:1992, 1-2.a
TEC none total electron count (areal electron density) At a given point in space, the number of electrons incident on a small sphere, divided by the cross-sectional area of that sphere.
1 TEC = 1016 1/m2 (exactly).		 AREAL_ENTITY_DENSITY 215 ISO 31-6:1992, 6-28.a  
TESLA T magnetic flux density (magnetic induction) The amount of magnetic flux through a unit area taken perpendicular to the direction of the magnetic flux.
1 T = 1 Wb/m2 = 1 kg/(s2 · A).		 MAGNETIC_FLUX-
_DENSITY		 216 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-19.a
thermodynamic critical magnetic flux density The critical flux density for disappearance of superconductivity in type I superconductors. ISO 31-13:1992, 13-37.a  
TONNE t mass 1 t = 1 000 kg (exactly). MASS 218 ISO 31-0:1992, Table 4 ISO 31-3:1992, 3-1.b
TONNE_PER_CUBIC_METRE t/m3 volumic mass (mass density) The mass divided by the volume.
1 t/m3 = 103 kg/m3 (exactly).		 VOLUMIC_MASS 219 ISO 31-3:1992, 3-2.b  
UNIFIED_AMASS_UNIT u molecular mass The value of the unified atomic mass unit is determined experimentally and is equal to (1 / 12) of the mass of an atom of the nuclide 12C; 1 u = 1,660 540 x 10-27 kg (approximately). MASS 220 ISO 31-0:1992, Table 6 ISO 31-8:1992, 8-31.b; ISO 31-9:1992, 9-4.b; ISO 31-9:1992, 9-5.b; ISO 31-9:1992, 9-28.b
UNITLESS 1 (often omitted) special (pure number) 1. PURE_NUMBER 221 ISO 31-0:1992, 2.3.3  
VOLT V electric potential The potential measured by the energy of a unit positive charge at a point, expressed relative to an equipotential surface, generally the surface of the <EARTH>, that has zero potential.
1 V = 1 W/A = 1 (m2 · kg)/(s3 · A).		 ELECTRIC_POTENTIAL 222 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-6.a
electromotive force The energy supplied by a source divided by the electric charge transported through the source.
1 V = 1 W/A = 1 (m2 · kg)/(s3 · A).		 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-6.a
Peltier coefficient The Peltier heat power developed at a junction, divided by the electric current flowing from substance A to substance B. ISO 31-13:1992, 13-23.a  
VOLT_AMP V · A apparent power In electric power technology, active power is expressed in watts (W), apparent power in volt amperes (V · A) and reactive power in vars (var).
1 V · A = 1 (m2 · kg)/(s3 · A).		 APPARENT_POWER 223 ISO 31-5:1992, 5-50.a ISO 1000:1992, Annex A, 5-49
VOLT_PER_KELVIN V/K Seebeck coefficient The thermoelectromotive force between two substances divided by the temperature of their hot junction.
1 V/K = 1 (m2 · kg)/(s3 · A · K).		 SEEBECK_COEFFICIENT 224 ISO 31-13:1992, 13-22.a  
Thomson coefficient The Thomson heat power developed divided by the electric current and temperature difference. ISO 31-13:1992, 13-24.a  
VOLT_PER_METRE V/m electric field strength The force, exerted by electric field on an electric point charge, divided by the electric charge.
1 V/m = 1 N/C = 1 (m · kg)/(s3 · A).		 ELECTRIC_FIELD-
_STRENGTH		 225 ISO 31-5:1992, 5-5.a  
VOLT_SQD_PER_KELVIN_SQD V2/K2 Lorenz coefficient The thermal conductivity divided by the electrical conductivity and the thermodynamic temperature.
1 V2/K2 = 1 (m4 · kg2)/(s6 · A2 · K2).		 LORENZ_COEFFICIENT 226 ISO 31-13:1992, 13-19.a  
WATT W heat flow rate The rate at which heat crosses a given surface. POWER 227 ISO 31-4:1992, 4-7.a  
power The rate of energy transfer.
1 W = 1 J/s = 1 (m2 · kg)/s3.		 ISO 31-0:1992, Table 2 ISO 31-3:1992, 3-27.a; ISO 31-5:1992, 5-35.a
radiant power (radiant energy flux) The power emitted, transferred or received as radiation. ISO 31-6:1992, 6-10.a  
sound power The power emitted, transferred or received as sound waves. ISO 31-7:1992, 7-16.a  
WATT_HOUR W · h electrical active energy The practical unit of energy in electrical systems.
1 W · h = 3 600 J (exactly).		 ENERGY 228 ISO 31-5:1992, 5-52.b  
WATT_PER_KELVIN W/K thermal conductance The heat flow rate divided by temperature difference; the reciprocal of thermal resistance.
1 W/K = 1 (m2 · kg)/(s3 · K).		 THERMAL_CONDUCTANCE 229 ISO 31-4:1992, 4-13.a  
WATT_PER_METRE_K W/(m · K) thermal conductivity The areic heat flow rate divided by temperature gradient.
1 W/(m · K) = 1 (m · kg)/(s3 · K).		 THERMAL_CONDUCTIVITY 230 ISO 31-4:1992, 4-9.a  
WATT_PER_SQ_CM_SEC W/(cm2 · s) radiant exitance rate At a point on a surface, the radiant energy flux leaving the element of the surface over an interval of time, divided by the area of that element and that time.
1 W/(cm2 · s) = 10-4 W/(m2 · s) (exactly).		 RADIANT_EXITANCE-
_RATE		 231 ISO 31-0:1992, 2.3.2.3 (derived)  
WATT_PER_SQ_M_HZ W/(m2 · Hz) flux density (frequency dependent) The amount of a given type of radiation that crosses a specified area within a specified period.
1 W/(m2 · Hz) = 1 kg/s2.		 FLUX_DENSITY 232 ISO 31-0:1992, 2.3.1 and 2.3.2 (derived)  
WATT_PER_SQ_M_K_FOURTH_PWR W/(m2 · K4) Stefan-Boltzmann constant The constant relating the power per unit area emitted by a radiating black body to its thermodynamic temperature.
1 W/(m2 · K4) = 1 kg/(s3 · K4).		 STEFAN_BOLTZMAN-
_CONSTANT		 233 ISO 31-6:1992, 6-18.a  
WATT_PER_SQ_METRE W/m2 areic heat flow rate (density of heat flow rate) The heat flow rate divided by area.
1 W/m2 = 1 kg/s3.		 IRRADIANCE 234 ISO 31-4:1992, 4-8.a  
energy fluence rate (energy flux density) At a given point in space, the sum of the energies, exclusive of rest energy, of all the particles incident on a small sphere in a small time interval, divided by the cross-sectional area of that sphere and by the time interval. ISO 31-10:1992, 10-11.a  
irradiance At a point on a surface, the radiant energy flux incident on (or leaving) an element of the surface, divided by the area of that element. ISO 31-6:1992, 6-16.a  
Poynting vector The vector product of electric field strength and magnetic field strength. ISO 31-5:1992, 5-31.a  
radiant energy fluence rate At a given point in space, the radiant flux incident on a small sphere over a short time interval, divided by the cross-sectional area of that sphere and that time. ISO 31-6:1992, 6-12.a  
radiant exitance At a point on a surface, the radiant energy flux incident on an element of the surface, divided by the area of that element. ISO 31-6:1992, 6-15.a  
sound intensity For unidirectional sound power, sound power through a surface normal to the direction of propagation divided by the area of the surface. ISO 31-7:1992, 7-17.a  
WATT_PER_SQ_METRE_K W/(m2 · K) coefficient of heat transfer The heat flow rate divided by area.
1 W/(m2 · K) = 1 kg/(s3 · K).		 COEFFICIENT_HEAT-
_TRANSFER		 235 ISO 31-4:1992, 4-10.a  
WATT_PER_SQ_METRE_MICRON W/(m2 · μm) integrated spectral radiance At a point on a surface and integrated over all directions, the radiant intensity of an element of the surface, divided by the area of the orthogonal projection of this element on a plane perpendicular to the given direction, as a function of radiant wavelength.
1 W/(m2 · μm) = 1 kg/(s3 · μm).		 SPECTRAL_RADIANCE-
_INTEGRATED		 236 ISO 31-0:1992, 2.3.2.2 (derived)  
WATT_PER_SQ_METRE_SEC W/(m2 · s) radiant exitance rate At a point on a surface, the radiant energy flux leaving the element of the surface over an interval of time, divided by the area of that element and that time.
1 W/(m2 · s) = 1 kg/s4.		 RADIANT_EXITANCE-
_RATE		 237 ISO 31-0:1992, 2.3.2.2 (derived)  
WATT_PER_SQ_METRE_SR W/(m2 · sr) total radiance At a point on a surface and in a given direction, the spectrally integrated radiant intensity of an element of the surface, divided by the area of the orthogonal projection of this element on a plane perpendicular to the given direction.
1 W/(m2 · sr) = 1 kg/(s3 · sr).		 RADIANCE 238 ISO 31-6:1992, 6-14.a  
WATT_PER_SQ_METRE_SR_MICRON W/(m2 · sr · μm) spectral radiance At a point on a surface and in a given direction, the radiant intensity of an element of the surface, divided by the area of the orthogonal projection of this element on a plane perpendicular to the given direction, as a function of radiant wavelength.
1 W/(m2 · sr · μm) = 1 kg/(s3 · sr · μm).		 SPECTRAL_RADIANCE 239 ISO 31-0:1992, 2.3.2.2 (derived)  
WATT_PER_STERADIAN W/sr radiant intensity In a given direction from a source, the radiant energy flux leaving the source, or an element of the source, in an element of solid angle containing the given direction, divided by that element of solid angle.
1 W/sr = 1 (m2 · kg)/(s3 · sr).		 RADIANT_INTENSITY 240 ISO 31-6:1992, 6-13.a  
WATT_SECOND W · s electrical active energy The practical unit of energy in electrical systems.
1 W · s = 1 J (exactly).		 ENERGY 241 ISO 31-0:1992, Table 2 ISO 31-0:1992, 2.3.2.2 (derived)
WATT_SQ_METRE W · m2 first radiation constant The constant c1 in the expression for the spectral concentration of the radiant exitance of a full radiator (black body).
1 W · m2 = 1 (m4 · kg)/s3.		 FIRST_RADIATION-
_CONSTANT		 242 ISO 31-6:1992, 6-19.a  
WEBER Wb magnetic flux Across a surface element, the scalar product of the magnetic flux density and the surface element.
1 Wb = 1 V · s = 1 (m2 · kg)/(s2 · A).		 MAGNETIC_FLUX 243 ISO 31-0:1992, Table 2 ISO 31-5:1992, 5-20.a
WEBER_PER_METRE Wb/m magnetic vector potential A vector quantity, the rotation (curl) of which is equal to the magnetic flux density.
1 Wb/m = 1 (m · kg)/(s2 · A).		 MAGNETIC_VECTOR-
_POTENTIAL		 244 ISO 31-5:1992, 5-21.a