Tesla (unit)
SI unit of magnetic flux density, named after Nikola Tesla.
The tesla (symbol: T) is the SI unit for magnetic flux density, also known as the magnetic B-field. One tesla equals one weber per square meter. The unit was introduced at the General Conference on Weights and Measures in 1960 and named after Nikola Tesla, a Serbian-American engineer, following a proposal by Slovenian engineer France Avčin. Like all SI units named after a person, the symbol is capitalized (T), but the unit name is written in lowercase (tesla).
A particle with a charge of one coulomb moving at one meter per second perpendicular to a magnetic field of one tesla experiences a force of one newton, as described by the Lorentz force law. This gives the relationship: T = (N·s) / (C·m). In SI base units, one tesla is expressed as T = kg / (A·s²), where A is amperes, kg is kilograms, and s is seconds.
As an SI derived unit, the tesla can also be expressed in other units. A magnetic flux of one weber through a one-square-meter surface equals a flux density of one tesla: T = Wb / m². Using the definition of a coulomb (C = A·s), the tesla becomes T = N / (A·m). From the relationship between newtons and joules (J = N·m), it follows that T = J / (A·m²). And since a weber equals volt-seconds (Wb = V·s), the tesla is also T = (V·s) / m².
The CGS system has a similar unit called the gauss. One tesla equals 10⁴ gauss, though the units have subtle differences, and the gauss is not acceptable for use with SI units per NIST guidelines. The gamma (γ), once used in geophysics and defined as 10⁻⁵ gauss, equals 10⁻⁹ tesla; the modern convention is to use the nanotesla (nT) instead. The 2019 revision of the SI changed the definition of the ampere, which altered the definition of the tesla by 106.67 parts in 10⁹. This revision also changed the permeability constant (μ₀), making conversions between SI units like the tesla and CGS units like the gauss slightly uncertain, and their use is now discouraged in scholarly journals.
Examples of magnetic field strengths, listed in ascending order: 25,000–65,000 nT for Earth’s magnetic field at its surface; 40 μT (4×10⁻⁵ T) when walking under a high-voltage power line; 5 mT (5×10⁻³ T) for a typical refrigerator magnet; and 0.3 T.
- unit_name
- Tesla
- symbol
- T
- quantity
- Magnetic flux density (B)
- system
- International System of Units (SI)
- named_after
- Nikola Tesla
Quick Facts
- Standard
- SI
- Quantity
- magnetic flux density
- Symbol
- T
- Namedafter
- Nikola Tesla
- Extraheader
- In SI base units
- Extralabel
- 1 T
- Extradata
- = 1 kg⋅s / −2 / ⋅A / −1
- Extraheader2
- In Gaussian units
- Extradata2
- corresponds to e=4 · u=G
Facts from the source article.
Lore & Background
The tesla (symbol: T) is the SI unit of magnetic flux density, also known as the magnetic B-field. One tesla is defined as one weber per square metre. Its definition is rooted in the Lorentz force law: a particle with a charge of one coulomb, moving perpendicularly through a magnetic field of one tesla at a speed of one metre per second, experiences a force of one newton. In SI base units, this equates to one kilogram per ampere per second squared. The unit can also be expressed as one newton per ampere-metre, one joule per ampere-square metre, or one volt-second per square metre. The tesla was announced at the General Conference on Weights and Measures in 1960 and named after Serbian-American engineer Nikola Tesla, following a proposal by Slovenian engineer France Avčin. As with all SI units named after a person, the symbol is uppercase (T) while the unit name is written in lowercase (tesla). A related non-SI unit is the gauss, where one tesla equals 10,000 gauss; however, the gauss is not acceptable for use with SI units. The gamma (γ), formerly used in geophysics and defined as 10⁻⁵ gauss, corresponds to 10⁻⁹ tesla, now expressed as the nanotesla (nT). The 2019 revision of the SI changed the definition of the ampere, altering the definition of the tesla by 106.67 parts in 10⁹ and introducing slight uncertainty in conversions between the tesla and CGS units like the gauss.
Reader's Guide
The tesla is the SI unit of magnetic flux density, symbolized by an uppercase T but written in lowercase when spelled out. It was formally adopted in 1960 at the General Conference on Weights and Measures, named for Nikola Tesla following a proposal by Slovenian engineer France Avčin. One tesla equals one weber per square meter. The unit can be defined through the Lorentz force law: a particle carrying a charge of one coulomb moving perpendicularly through a one-tesla field at one meter per second experiences a force of one newton. Expressed in base SI units, one tesla equals one kilogram per second squared per ampere. The 2019 revision of the SI redefined the ampere, which altered the tesla’s definition by about 106.67 parts per billion and also changed the permeability constant, making conversions between the tesla and the older CGS gauss unit (10,000 gauss per tesla) slightly uncertain; such conversions are now discouraged in scholarly work. The gamma, once used in geophysics and equal to 10⁻⁵ gauss, corresponds to 10⁻⁹ tesla and has been replaced by the nanotesla. Magnetic field strengths span many orders of magnitude: Earth’s surface field is roughly 40 microtesla, a typical refrigerator magnet produces about 5 millitesla, medical MRI systems operate between 1.5 and 3 tesla (with experimental units up to 17 tesla), the Large Hadron Collider’s magnets reach 8 tesla, and the strongest continuous-field magnets have achieved 45 tesla. Non-destructive pulsed magnets have reached 97.4 tesla, while the magnetic field of a typical white dwarf star is around 100 tesla. The highest fields are found on magnetar neutron stars, ranging from 100 million to 100 billion tesla. The Schwinger limit, above which the electromagnetic field becomes nonlinear, is about 10⁹ tesla.
Did You Know?
- One tesla equals one weber per square metre.
- The tesla is named after Serbian-American electrical and mechanical engineer Nikola Tesla, upon the proposal of Slovenian electrical engineer France Avčin.
Frequently Asked Questions
Who is Tesla (unit)?
The tesla is the SI unit that measures magnetic flux density, often called the magnetic B-field. It carries the symbol T (capital) while the unit name itself is always written in lowercase.
What are Tesla (unit)'s powers/role?
One tesla corresponds to one weber of magnetic flux spread over one square metre of surface. In practice it tells you how tightly packed the magnetic field lines are at a particular point.
Why is Tesla (unit) important?
It gives the entire scientific and engineering community a single, agreed-upon standard for expressing magnetic field strength. The name also keeps Nikola Tesla, the Serbian-American electrical and mechanical engineer, permanently linked to the measurement of magnetism.
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