Larmor

Larmor refers to Joseph Larmor (1857–1942), an Irish-born British physicist who made significant contributions to classical theories of magnetism and the early development of electron theory. His work established the concept that magnetic moments in a magnetic field precess around the field direction, a phenomenon now known as Larmor precession. The idea and its governing equation became foundational in several areas of physics, including spectroscopy and magnetic resonance.

Larmor precession describes how a magnetic moment μ in a uniform magnetic field B experiences a torque and precesses about the field axis with angular frequency ω given by ω = γ B, where γ is the gyromagnetic ratio of the particle. This precession underlies the behavior of nuclei and electrons in magnetic fields and is central to techniques such as nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).

The term Larmor radius (or gyroradius) refers to the radius of the circular motion traced by a charged particle moving perpendicular to a uniform magnetic field. For a non-relativistic particle with charge q and mass m, r_L = m v_perp / (|q| B), where v_perp is the velocity component perpendicular to B. The corresponding Larmor frequency and radius are key parameters in plasma physics and beam dynamics.

In summary, Larmor denotes both the physicist who introduced these concepts and the resulting foundational ideas—Larmor precession, Larmor frequency, and Larmor radius—that describe the behavior of magnetic moments and charged particles in magnetic fields.