SI is capable of measuring anything from the tiniest particles to the largest objects in the universe. While it may sound technical and scientific, there are practical benefits of tiny measurements in some everyday products. Here, Ronnie Cohen takes a look.
The thickness of laminated sheets is described and marketed in microns, an obsolete term for micrometres (millionths of a metre). Similarly, one thing to look for in quality office paper is its thickness. On the ZX printer website, for example, they give the thickness of printing paper in grams per square metre and in millimetres (Source: https://www.zxprinter.com/support/paper-thickness.html). I suspect the reason for their use of millimetres rather than micrometres is that millimetres are a more familiar to the general public. Familiarity comes with usage and millimetres are a lot more common. For our readers, I am converting the millimetres to micrometres. I give you a few of the tiny measurements to show how versatile the metric system in measuring the extremely small. On the conversion tables on their website, 80 g/m² art paper = 65 micrometres, 60 g/m² matt coated paper = 60 micrometres and 30 g/m² bible paper = 40 micrometres.
Tiny medical doses and ingredients are often expressed in micrograms (millionths of a gram). Micrograms are also used in medical advice to the general public. For example, the NHS advises “Babies up to the age of 1 year need 8.5 to 10 micrograms of vitamin D a day.”. You can find vitamin D tablets on sale containing doses as small as 10 micrograms.
Semiconductor manufacturers compete to make increasingly sophisticated computer chips. The transistor gate lengths of computer chips are measured in nanometres (billionths of a metre). The Wikipedia page for Semiconductor Device Fabrication shows that manufacturers used a 10 micrometre manufacturing process in 1971. This figure has come down to 7 nanometres by 2018 and is predicted to come down further to 5 nanometres in 2020 and to 3 nanometres in 2022.
Solar cells are made using silicon wafers that are between 180 and 350 micrometres thick. Solar cells can be found in products such as solar panels and many solar-powered products such as calculators, watches, radios and lamps. You can find a more comprehensive list of solar-powered products on Wikipedia (Source: https://en.wikipedia.org/wiki/List_of_solar-powered_products).
In the field of nanotechnology, nanoparticles are manipulated to produce better, stronger and more durable products. Nanoparticles are tiny microscopic particles and typically sized between 1 and 100 nanometres. Carbon nanotubes, a product of nanotechnology, have diameters measured in nanometres with some as little as 1 nanometre across (Source: https://www.britannica.com/science/carbon-nanotube). Carbon nanotubes are used in sports products, batteries and medical applications. They are used in a range of other common products as well. Nanotechnology has practical applications and has been applied to many products in the clothing, electronics, materials, healthcare, energy, transport and environment sectors. And this is not a comprehensive list.
Sources:
- https://www.zxprinter.com/support/paper-thickness.html
- https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
- https://en.wikipedia.org/wiki/Nanotechnology
- https://en.wikipedia.org/wiki/Semiconductor_device_fabrication
- https://en.wikipedia.org/wiki/Solar_cell
- https://en.wikipedia.org/wiki/List_of_solar-powered_products
- https://www.britannica.com/science/carbon-nanotube
- https://www.understandingnano.com/nanotubes-carbon.html
- https://www.microscopemaster.com/nanotechnology-products.html
- http://trynano.org/
Metric Views 
One of the limitations of actually seeing the various things that Ronnie has written about using a conventional microscope is the wavelength associated with light. Red light has a wavelength that is typically up to 760 nanometres and violet light has a wavelength that is typically more than 380 nanometres. If the object that is being illuminated by light is smaller than these wavelengths, the light will not be reflected and you will not be able to see it. Electron microscopes do not use visible light which is why they can photpgraph objects that are smaller.
In practice this means that you cannot see anything that is smaller than 0.001 millimetres unless you use an electron microscope.
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You missed the opportunity to mention a couple of hot topics. My covid-19 face mask came complete with a PM2.5 filter, ie one that filters out particulates down to 2.5 ?m. Pollution in the form of particulates are a big concern at the moment, the two key measurements being PM2.5 and PM10 (PM10 being 10 ?m). Maximum values for these have been set by both the EU and the WHO. In addition to be used to define air quality, they also form part of the European emissions standards for cars (Euro1, Euro2 etc). The quantity of each is measured in ?g/m³.
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Here we come across one of the fundamental problems we all face with using SI symbols.
Unless and until there is a universal, world wide method adopted to print non-ASCII characters in and on all platforms and all word processing applications we face a number of variations and interpretations.
Wordpress (as used on this site) accepts only ASCII characters, unicode (143,859 characters according to Wikipedia!) is stored as ASCII interpretation (Alt+whatever) , and it is up to the front end and back end programmes to use the same coding to get the same end to end result.
From this we will probably always have to spell micro (µ) and degree (°) in ASCII standard form.
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Martin,
Were the limits of red and violet light of 760 nm and 390 nm respective chosen based on any particular criteria? I ask because it appears to me to be 3 inches/1 000 000 and 1.5 inches/1 000 000. It seems more than just coincidental. Like maybe in the early days the wavelengths were determined in inches and just soft converted to nanometres.
Robert,
Why is there a 2.5 µm size and not a 1, 2, 3, 4, etc, in whole numbers micrometre sizes? It almost seems like someone was trying to come close to 1 inch/10 000.
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I wonder why ‘micro’ was singled out to have a Greek letter. It certainly does cause problems. It was a problem when documents were bashed out on a typewriter, but even today engineering software very often substitutes it with a lower case u. Being an engineer I considered making that substitution, but thought it might trigger someone (I’ve seen it happen). So, not having it on my keyboard, I copied and pasted mu from Wikipedia, and ended up with a question mark (even though mu displayed OK in the edit box). I tried using the contact form to ask if it could be fixed by one means or another, but it seems contact form messages are emailed to an account that bounces. But Brian and Daniel have managed to get mu to to display, so I will copy and paste the one they used and see what happens. Fingers crossed…
The regulated particle sizes are specified and named using SI, but I don’t know the reasoning behind making them 10 µm and 2.5 µm. I would point out that 2.5 µm is exactly one quarter of 10 µm, so I wouldn’t assume it’s an inch thing. That said, maybe they were chosen just to keep everyone reasonably happy, no matter which system they used.
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@Daniel Jackson
The length of the metre was defined in the 1790’s. Light waves were unknown then – they were only discovered a few decades later and it was only in the 1860’s that Anders Jonas Ångström catalogued the various colours and it was by measurement that the limits of 760 nm and 390 nm were established. These limts are of course approximate – the actual limits depends on the individual;s eyes.
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@Robert
Both the “micro” and the “ohm” (another Greek letter) symbols date from the nineteenth century. The typewriter is not particularly well suited to writing out mathematical equations so mathematicians added any symbols to any scripts by hand. I recall doing this in reports that I wrote at the Diamond Research Laboratory, Johannesburg in the 1970’s.
If you visit https://en.wikipedia.org/wiki/Maxwell%27s_equations you can see how complex mathematical equations can become. Furthermore, other Greek letter that are in frerquent use are lambda (for wavelength), theta and phi for angles, rho for density, lower case sigma for standard deviation, upper case sigma for the summation symbol, lower case pi for 3.1415…., upper case pi for the product symbol, lower case delta to denote a small fraction of something, epsilon for a very small quantity etc.
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Martin,
Your response was very informative, but didn’t answer my question. I was inquiring that since the values you chose to mention, “380” and “760” in nanometres work out to be a sub-multiple of 1.5 and 3 inches, if Mr Ångström possibly did his measuring in decimal inches or Swedish tums and these were later converted to nanometres.
According to you, Mr Ångström did his research in the 1860s. It wasn’t until 1876 that Sweden according to the Wikipedia article on metrication began its metrication program. I would suspect that Mr Ångström may have used Swedish units of measure but he may also have used British units in order to make his discoveries understandable among British scientists of the time and even though the metric system was gaining ground in scientific circles was still in its infancy. It probably took to past the WW1 era for pre-metric units to be phased out of most scientific work.
The Swedish “tum” was just under 25 mm before 1863 and just under 30 mm after 1863. If he did his measuring in tums with the pre-1863 definition if was close enough to the English inch that the two units could be considered equal.
So, to conclude, do we know what units Mr Ångström recorded his findings in?
https://en.wikipedia.org/wiki/Metrication
https://en.wikipedia.org/wiki/Swedish_units_of_measurement
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@Daniel Jackson
If you read the Wikipedia article at https://en.wikipedia.org/wiki/Angstrom you will see that Ångström used metric units to the best of his ability, but that the definition of the metre (based on the original French metre of 1799) was too imprecise for his work, so he invented his own unit of measure that became known as the ångström. In Ångström’s view, the ångström was nominally 10^-8 centimetres. Ångström died in 1874 and in 1960 the metre was redefined such that the ångström became precisely 10^-8 centimetres.
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