# Micrometre

Last updated
Micrometre
a 6 μm diameter carbon filament,
compared to 50 μm diameter human hair
General information
Unit system metric
Unit of length
Symbolμm
Conversions
1 μm in ...... is equal to ...
SI units    1×10−6  m
Natural units    6.1877×1028  P
1.8897×104  a0
imperial/US  units   3.2808×10−6  ft
3.9370×10−5  in

The micrometre (International spelling as used by the International Bureau of Weights and Measures; [1] SI symbol: μm) or micrometer (American spelling), also commonly known by the previous name micron, is an SI derived unit of length equalling 1×10−6  metre (SI standard prefix "micro-" = 10−6); that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039  inch). [1]

The International Bureau of Weights and Measures is an intergovernmental organization that was established by the Metre Convention, through which member states act together on matters related to measurement science and measurement standards. The organisation is usually referred to by its French initialism, BIPM. The BIPM's headquarters is based at Sèvres, France. It has custody of the International Prototype of the Kilogram and houses the secretariat for this organization as well as hosting its formal meetings.

SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They are either dimensionless or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation.

Length is a measure of distance. In the International System of Quantities, length is any quantity with dimension distance. In most systems of measurement, the unit of length is a base unit, from which other units are derived.

## Contents

The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria, [1] and for grading wool by the diameter of the fibres. [2] The width of a single human hair ranges from approximately 10 to 200 μm. The longest human chromosome is approximately 10 μm in length.

Measurement is the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. The scope and application of measurement are dependent on the context and discipline. In the natural sciences and engineering, measurements do not apply to nominal properties of objects or events, which is consistent with the guidelines of the International vocabulary of metrology published by the International Bureau of Weights and Measures. However, in other fields such as statistics as well as the social and behavioral sciences, measurements can have multiple levels, which would include nominal, ordinal, interval and ratio scales.

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is thus the inverse of the spatial frequency. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. Wavelength is commonly designated by the Greek letter lambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.

The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life. Cells are often called the "building blocks of life". The study of cells is called cell biology.

## Examples

Between 1 μm and 10 μm:

A hypha is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.

A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote.

Spider silk is a protein fibre spun by spiders. Spiders use their silk to make webs or other structures, which function as sticky nets to catch other animals, or as nests or cocoons to protect their offspring, or to wrap up prey. They can also use their silk to suspend themselves, to float through the air, or to glide away from predators. Most spiders vary the thickness and stickiness of their silk for different uses.

Between 10 μm and 100 μm

• about 10–12 μm – thickness of plastic wrap (cling wrap)
• 10 to 55 μm – width of wool fibre [5]
• 17 to 181 μm – diameter of human hair [6]
• 70 to 180 μm – thickness of paper

Plastic wrap, cling film, shrink wrap, Saran wrap, cling wrap or food wrap is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time. Plastic wrap, typically sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container without adhesive. Common plastic wrap is roughly 0.0005 inches thick. The trend has been to produce thinner plastic wrap, particularly for household use, so now the majority of brands on shelves around the world are 8, 9 or 10 μm thick.

Wool is the textile fiber obtained from sheep and other animals, including cashmere and mohair from goats, qiviut from muskoxen, from hide and fur clothing from bison, angora from rabbits, and other types of wool from camelids; additionally, the Highland and the Mangalica breeds of cattle and swine, respectively, possess wooly coats. Wool consists of protein together with a few percent lipids. In this regard it is chemically quite distinct from the more dominant textile, cotton, which is mainly cellulose.

## SI standardization

The term micron and the symbol μ were officially accepted for use in isolation to denote the micrometre in 1879, but officially revoked by the International System of Units (SI) in 1967. [7] This became necessary because the older usage was incompatible with the official adoption of the unit prefix micro-, denoted μ, during the creation of the SI in 1960.

The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the ampere, kelvin, second, metre, kilogram, candela, mole, and a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units, such as lumen and watt, for other common physical quantities.

In the SI, the systematic name micrometre became the official name of the unit, and μm became the official unit symbol.

Nevertheless, in practice, "micron" remains a widely used term in preference to "micrometre" in many English-speaking countries, both in academic science (including geology, biology, physics, and astronomy) and in applied science and industry (including machining, the semiconductor industry, and plastics manufacturing).[ citation needed ] Additionally, in American English, the use of "micron" helps differentiate the unit from the micrometer, a measuring device, because the unit's name in mainstream American spelling is a homograph of the device's name. In spoken English, they may be distinguished by pronunciation, as the name of the measuring device is invariably stressed on the second syllable, whereas the systematic pronunciation of the unit name, in accordance with the convention for pronouncing SI units in English, places the stress on the first syllable.

Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also refer to the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.

Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species. Living organisms are open systems that survive by transforming energy and decreasing their local entropy to maintain a stable and vital condition defined as homeostasis.

Physics is the natural science that studies matter and its motion and behavior through space and time and that studies the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.

The plural of micron is normally "microns", though "micra" was occasionally used before 1950. [8] [9] [10]

## Symbol

The official symbol for the SI prefix micro- is a Greek lowercase mu (μ). [11] In Unicode, there is also a micro sign with the code point U+00B5 (µ), distinct from the code point U+03BC (μ) of the Greek letter lowercase mu. According to the Unicode Consortium, the Greek letter character is preferred, [12] but implementations must recognize the micro sign as well. Most fonts use the same glyph for the two characters.

## Notes and references

1. "micrometre". Encyclopædia Britannica Online . Retrieved 18 May 2014.
2. "Wool Fibre". "NSW Department of Education and Communities". Archived from the original (Word Document download) on June 17, 2016. Retrieved 18 May 2014.
3. Smith, D.J.; Gaffney, E.A.; Blake, J.R.; Kirkman-Brown, J.C. (25 February 2009). "Human sperm accumulation near surfaces: a simulation study" (PDF). Journal of Fluid Mechanics . Cambridge University Press. 621: 295. Bibcode:2009JFM...621..289S. doi:10.1017/S0022112008004953 . Retrieved 20 May 2012.
4. Ramel, Gordon. "Spider Silk". Archived from the original on 4 December 2008. Retrieved 14 December 2008. A typical strand of garden spider silk has a diameter of about 0.003 mm ... Dragline silk (about .00032 inch (.008 mm) in Nephila)
5. "Fibreshape applications". IST - Innovative Sintering Technologies Ltd. Retrieved 4 December 2008. Histogram of Fiber Thickness [micrometer]
6. The diameter of human hair ranges from 17 to 181 μm. Ley, Brian (1999). Elert, Glenn, ed. "Diameter of a human hair". The Physics Factbook. Retrieved 2018-12-08.
7. BIPM - Resolution 7 of the 13th CGPM 1967/68), "Abrogation of earlier decisions (micron, new candle.)"
8. Proceedings of the Royal Society of Queensland. Part I. XIX. H. Pole & Co. via Google Books.
9. Bigalow, Edward Fuller; Agassiz Association (1905). The Observer. 7–8 via Google Books.
10. 10 micra/10 microns (Start at 1885; before that, the word "micron", singular or plural, was rare)
11. "Prefixes of the International System of Units". International Bureau of Weights and Measures . Retrieved 9 May 2016.
12. Beeton, Barbara; Freytag, Asmus; Sargent, Murray III (30 May 2017). "Unicode® Technical Report #25". Unicode Technical Reports. Unicode Consortium. p. 11.
• The dictionary definition of micrometre at Wiktionary