The "archin" is an obsolete unit of length that was historically used in Russia and other parts of the former Soviet Union. The length of an archin varied by region and over time, but it was typically around 28 inches or approximately 71 centimeters. In some regions, an archin could be slightly shorter or longer.
The archin was used for measuring cloth, textiles, and sometimes land. Like many traditional units of measurement, it has largely been replaced by more standardized systems, such as the metric system, in modern times. While the archin is no longer commonly used for official measurements, it may still be encountered in historical or traditional contexts in Russia and other former Soviet states.
The Bohr radius, often denoted as "a₀," is a fundamental physical constant in quantum mechanics and atomic physics. It is named after the Danish physicist Niels Bohr, who made significant contributions to our understanding of atomic structure.
The Bohr radius represents the average distance between the nucleus and the electron in the lowest energy state (ground state) of a hydrogen atom, or a hydrogen-like ion with a single electron (e.g., helium ion with only one electron remaining). It is a key parameter in the Bohr model of the hydrogen atom.
The Bohr radius is defined as:
a₀ = (4πε₀ħ²) / (me²),
where:
When you calculate the Bohr radius using these constants, you get a value of approximately 5.29177210903 x 10⁻¹¹ meters, or about 0.5292 angstroms (Å).
The Bohr radius is a critical parameter in understanding the structure of atoms, particularly hydrogen-like atoms. It provides a basic scale for the size of atomic orbitals and helps in describing the energy levels of electrons in these atoms.