Tesla (unit)

Definition and equivalent expressions

By definition, one tesla is equal to one weber per square metre. In SI base units and other common expressions, the tesla can be written as:

• 1 T = 1 Wb/m²
• 1 T = 1 N/(A·m)
• 1 T = 1 kg/(A·s²)

These relationships show that the tesla is a derived unit tied to mechanical and electrical base units. For historical and practical comparison, 1 tesla equals 10,000 gauss (a non-SI unit still used in some fields).

Typical magnitudes and examples

Magnetic fields vary widely in strength. Typical orders of magnitude include:

• Earth's magnetic field on the surface: tens of microtesla (µT).
• Small permanent magnets and magnetic sensors: millitesla (mT) to tens of mT.
• Magnetic resonance imaging (MRI) scanners used in medicine: commonly around 1.5 T to 3 T; higher-field clinical and research systems exceed several tesla.
• Specialized laboratory and accelerator magnets can reach many tesla; some research magnets produce tens of tesla for short durations.

Measurement and instruments

Magnetic flux density is measured with a variety of instruments suited to different ranges and sensitivities. Common methods include Hall-effect probes for straightforward field mapping, fluxgate and search-coil magnetometers for low-frequency and DC measurements, and superconducting quantum interference devices (SQUIDs) for extremely small fields. Calibration, temperature effects, and sensor orientation are important factors when quantifying a field in tesla.

History and name

The symbol and name tesla were adopted in the mid-20th century as part of the SI system. The unit honors Nikola Tesla, the inventor and electrical engineer, recognizing his contributions to alternating current electrical systems and electromagnetic research. The formal adoption of the tesla as an SI derived unit occurred through international metrology bodies that standardize unit names and symbols.

Distinctions and related quantities

It is important to distinguish between magnetic flux density (B, measured in tesla) and magnetic field strength (H, measured in amperes per metre, A/m). Magnetic flux (total magnetic flux through a surface) is measured in webers (Wb), while magnetic susceptibility and permeability relate B and H within materials. Practical applications—such as design of electrical machines, particle accelerators, magnetic shielding, and biomedical imaging—use these related quantities together to characterize and control magnetic behavior.

For further technical details, consult primary references such as the SI Brochure and specialized texts on electromagnetism: SI and unit definitions, magnetic field concepts, weber and magnetic flux, Nikola Tesla biography, and history of SI unit adoption.