In the field of atomic and molecular physics, an "atomic unit of length" is a unit of measurement that is used to express distances at the atomic and molecular scale in a dimensionless way. It is part of a system of atomic units (a.u.) that simplifies calculations involving fundamental physical constants and properties of atoms and molecules.
The atomic unit of length (a.u. of length) is defined in terms of the Bohr radius (a₀), which is a fundamental constant in atomic physics. The Bohr radius is approximately 0.52917721067 angstroms (Å) or 5.2917721067 x 10^-11 meters (m).
In atomic units, the Bohr radius is set to exactly 1 a.u. of length. Therefore, when using atomic units, distances are expressed relative to the Bohr radius, and the value of 1 a.u. of length corresponds to the typical size scale of atomic and molecular structures.
The use of atomic units simplifies many quantum mechanical calculations and allows physicists and chemists to work with dimensionless quantities, making it easier to compare and analyze atomic and molecular properties.
A "famn" is a historical unit of length used for measuring depth or distance in nautical and maritime contexts. The term "famn" is of Swedish origin and was widely used in Scandinavian countries and regions with maritime traditions.
The exact length of a famn could vary by region and historical period, but it was typically around 1.8 to 2.2 meters (approximately 5.9 to 7.2 feet). It was commonly used for measuring water depth when navigating, anchoring, or fishing.
Like many historical units of measurement related to nautical and maritime activities, the use of the famn has largely been replaced by modern and standardized systems, such as meters or feet, for precise measurements in navigation and marine industries. However, you may still encounter the term "famn" in historical or traditional maritime contexts.