Micrometre
Videos
The micrometre is a unit of length in the International System of Units equalling 10−6 metre ; that is, one millionth of a metre. It is also known as the micron.
A 6 μm diameter carbon filament above a 50 μm diameter human hair
How big is 1 micrometre?
Parts-per notation
Videos
In science and engineering, parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction.
Fluorescein aqueous solutions, diluted from 10000 to 1 part per million in intervals of ten-fold dilution. At 10000 ppm the solution is a deep red colour. As the concentration decreases, the colour becomes greenish-orange, then a vibrant yellowish-green, with the final 1 ppm sample a very pale yellowish-green.
