Tesla

The tesla (symbol T) is the SI unit of magnetic flux density. It can be written several equivalent ways: 1 T = 1 Wb/m² (one weber per square metre) = 1 N/(A·m) = 1 V·s/m² = 1 kg/(A·s²). The most physically intuitive of these is the force-per-current-per-length form: a wire carrying one ampere, perpendicular to a one-tesla field, experiences a sideways force of one newton per metre of length.

A tesla is a strong field by everyday standards. Earth's surface magnetic field is only about 25–65 microtesla, depending on latitude. A refrigerator magnet is around 5 millitesla at its surface. A typical hospital MRI scanner runs at 1.5 or 3 tesla. The strongest continuous fields produced in the laboratory — using hybrid superconducting and resistive magnets at the National High Magnetic Field Laboratory — reach about 45 tesla. Pulsed magnets driven by capacitor banks can briefly exceed 100 T, and explosively driven flux-compression rigs have hit several thousand tesla for microseconds before destroying themselves. The most extreme natural magnetic fields, on the surface of magnetar neutron stars, are around 10¹¹ T.

The non-SI unit gauss (1 G = 10⁻⁴ T) survives in geophysics and astronomy, where it is more conveniently sized for naturally occurring fields. The tesla replaced the gauss as the SI primary unit in 1960 when the General Conference on Weights and Measures adopted the MKSA (now SI) system formally. The unit was named after Nikola Tesla, the Serbian-American inventor and engineer whose AC induction motor and polyphase electric power systems form the foundation of modern electrical infrastructure.

The unit was officially adopted at the 11th General Conference on Weights and Measures in 1960, named after Nikola Tesla (1856–1943) in recognition of his contributions to electrical engineering and AC power. It replaced the gauss (CGS unit) as the primary SI unit of magnetic flux density. The choice of name was politically delicate — Tesla had died penniless and largely forgotten in 1943, and the 1960 honour was part of a broader rehabilitation of his reputation that had been gathering pace through the 1950s.