Petameter
A petameter (Pm) is a unit of length in the metric system, equal to 1 quadrillion meters (1 petameter = 10¹⁵ meters). This unit is extremely large and is used mainly in astronomy and theoretical physics to describe vast distances, such as those between stars or galaxies. For example, one petameter is about 105.7 light years. Since it measures such enormous distances, the petameter is not used in everyday life or common scientific applications—it’s mostly used in discussions about the scale of the universe.
Bohr Radius
The Bohr radius is a fundamental physical constant that represents the average distance between the nucleus and the electron in a hydrogen atom in its ground state, according to the Bohr model of the atom.
Its value is approximately 5.29177 × 10⁻¹¹ meters (about 0.529 angstroms).
Named after physicist Niels Bohr, who introduced the model in 1913.
It sets a natural length scale in atomic physics and quantum mechanics.
Used to describe atomic sizes and electron orbitals.
Key facts:
Bohr radius ≈ 5.29 × 10⁻¹¹ m
Represents the typical size of a hydrogen atom’s electron orbit
Fundamental to quantum physics and atomic structure
The Bohr radius is essential for understanding atomic dimensions and quantum behavior of electrons.