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SI units

the units of measurement generally accepted for all scientific and technical uses; together they make up the International System of Units. (See also metric system.) The abbreviation SI, from the French Système International d'Unités, is used in all languages. There are seven base SI units, defined by specified physical measurements, and two supplementary units. Units are derived for any other physical quantities by multiplication and division of the base and supplementary units. The derived units with special names are shown in the accompanying table.

SI is a coherent system. This means that units are always combined without conversion factors. The derived unit of velocity is the meter per second (m/s); the derived unit of volume is the cubic meter (m3). If you know that pressure is force per unit area, then you know that the SI unit of pressure (the pascal) is the unit of force divided by the unit of area and is therefore equal to 1 newton per square meter.

The metric prefixes can be attached to any unit in order to make a unit of a more convenient size. The symbol for the prefix is attached to the symbol for the unit, e.g., nanometer (nm) = 10−9 m. The units of mass are specified in terms of the gram, e.g., microgram (μg) = 10−9 kg.

Only one prefix is used with a unit; the use of units such as the millimicrometer is no longer acceptable. When a unit is raised to a power, the power applies to the prefix as well, e.g., a cubic millimeter (mm3) = 10−9 m3. When a prefix is used with a ratio unit, it should be in the numerator rather than in the denominator, e.g., kilometers/second (km/s) rather than meters/millisecond (m/ms). Only prefixes denoting powers of 103 are normally used. Hecto-, deka-, deci-, and centi- are usually attached only to the metric system units gram, meter, and liter.

Owing to the force of tradition, one noncoherent unit, the liter, equal to 10−3 m3, or 1 dm3, is generally accepted for use with SI. The internationally accepted abbreviation for liter is the letter l; however, this can be confused with the numeral 1, especially in typescript. For this reason, the capital letter L is also used as a symbol for liter. The lower case letter is generally used with prefixes, e.g., dl, ml, fl. The symbols for all other SI units begin with a capital letter if the unit is named after a person and with a lower case letter otherwise. The name of a unit is never capitalized.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


William Thomson, Scottish physicist, 1824-1907. See: kelvin, Kelvin scale.

kel·vin (K),

A unit of thermodynamic temperature equal to 273.16-1 of the thermodynamic temperature of the triple point of water. See: Kelvin scale.
[Lord Kelvin]
Farlex Partner Medical Dictionary © Farlex 2012


(K) (kel'vin)
A unit of thermodynamic temperature equal to 1/273.16 of the thermodynamic temperature of the triple point of water.
See also: Kelvin scale
[Lord Kelvin]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
Outdoor light begins to get bluish at about 5,600 degrees Kelvin and goes up from there.
However, UCLA noted that the hydrogen fuel must be stored at temperatures of approximately 77 degrees Kelvin.
Temperatures at the its core can reach 7500 degrees Kelvin - and that is hotter than the surface of the sun#SATURN THE planet - 'rock' No.
It was discovered that temperatures inside a collapsing bubble can reach 20,000 degrees Kelvin, which is about four times hotter than the surface of the sun.
(Note both of these temperatures are in degrees Kelvin.) To is the characteristic temperature for data retention that embodies dielectric, field strength and charge loss effects.
DEGREES KELVIN: A Tale of Genius, Invention, and Tragedy.
Back in the lab, they created a ceramic compound that superconducted at the highest temperature then known: 30 degrees Kelvin. The rest, as they say, is history; Muller and Bednorz won the Nobel Prize and triggered a flurry of activity in superconductivity that continues to this day.
In addition, proper color temperature is important: Fluorescent lighting at 3,500 degrees Kelvin is ideal.
The lowercase k is used to avoid confusion with the uppercase K used for degrees Kelvin. Since the actual units of Hz are 1/sec, Boltzmann's constant can also be stated in the linear-form units watt/HzK or in the dB units dBW/HzK.
Two critical temperatures are measured: 1) the cryoshield is cooled to approximately 100 degrees Kelvin, and 2) the inner cryopanel is cooled to approximately 18 degrees Kelvin.
They produce a white light (3,000 to 4,000 degrees Kelvin) with a color rendering index of 6575.
Upon detonation of an energetic solid, shock waves propagate at several kilometers per second, temperatures rise to several thousand degrees Kelvin, and pressures peak at several hundred thousand atmospheres.