## Specific gravity

The specific gravity of a substance is the ratio of the substance’s density to the density of water. The density of water is 1 gram per cubic centimeter (1 g/cm3), so the specific gravity of a substance is simply its density in grams per cubic centimeter divided by 1. For example, the density of gold … Read more

## Permeability of free space (a vacuum)

The permeability of free space (a vacuum) is a measure of the ease with which a magnetic field can penetrate a material. It is a ratio of the magnetic flux density (B) to the magnetic field strength (H). The SI unit of permeability is the henry per meter (H/m). The permeability of free space is … Read more

## Candela (cd)

The candela is the SI unit of luminous intensity, or the power emitted by a light source in a particular direction. It is equal to one lumen per steradian. The candela is often used to measure the brightness of light sources, such as lamps and LEDs. It is also used in photometry, for measuring the … Read more

## Siemens (mho)

The Siemens (mho) is the unit of electrical conductance. It is the reciprocal of electrical resistance and is represented by the symbol “S”. One Siemens is equal to one ampere per volt. What has a unit of mho? A mho is a unit of electrical conductance. It is the reciprocal of an ohm, and is … Read more