Micrometer
From Halbeeg, the open encyclopedia · Af-Soomaali
20 languages
A micrometer (symbol: µm) is a unit of length in the International System of Units (SI). It is one millionth of a meter, or 10⁻⁶ m. It is equivalent to 1,000 nanometers and 0.001 millimeters.
The name derives from the SI prefix 'micro-' meaning one millionth, and 'meter'. The symbol µ is the Greek letter mu. When the µ character is not available, it is often written as 'um' or 'mkm'. Historically the unit was called 'micron', but this name was formally abandoned in 1967, although it remains in common use.
Measurement and comparison
The micrometer is suited for measuring objects too small for the unaided eye to see clearly. Human hair thickness is approximately ten micrometers. Red blood cells range from several micrometers. Most bacteria range from roughly one to several micrometers. The human eye can normally distinguish objects no smaller than about 40–50 µm.
Use in science and industry
The micrometer is the standard unit in biology for cellular measurement, microbiology, and microscopy. In manufacturing, precision engineering, and metal surface finishing, measurements are expressed in micrometers. The thickness of wire, film, and coatings is measured in this unit. In air quality science, particulate matter in the air is classified by size in micrometers, such as PM2.5 and PM10, denoting particles smaller than 2.5 µm and 10 µm respectively.
Light and wavelength measurement
Visible light has wavelengths ranging approximately from 0.4 to 0.7 micrometers. For this reason, optics and infrared radiation measurement consistently use the micrometer when measuring wavelength.
Measuring instruments
A micrometer screw gauge is a handheld instrument used to measure the thickness or length of objects with precision. The instrument itself differs from the unit; it typically measures to an accuracy of one micrometer or finer. Microscopes are fitted with graticules (scale gratings) calibrated in micrometers.