Weber (unit) — SI unit of magnetic flux

Overview

The weber (symbol: Wb) is the International System of Units (SI) derived unit used to measure magnetic flux. In practical terms, magnetic flux quantifies the total magnetic field passing through a given area. The unit's name honors the German physicist Wilhelm Eduard Weber (1804–1891). For a concise reference to SI conventions see SI units.

Definition and relations

By SI definition, one weber equals one volt-second: 1 Wb = 1 V·s. This follows from Faraday's law of electromagnetic induction: a time rate of change of magnetic flux of one weber per second through a circuit induces an electromotive force of one volt. The weber is related to magnetic flux density (field strength) by area: a flux density of 1 weber per square meter is 1 tesla, so 1 Wb/m² = 1 T. For more on magnetic flux itself, see magnetic flux.

Physical dimensions and alternate units

In base SI quantities the weber has the dimensions of mass × length² × time⁻² × current⁻¹ (M L² T⁻² I⁻¹), since volt has those dimensions per unit time. In the centimetre–gram–second (CGS) system the historical unit of magnetic flux is the maxwell; conversion between systems is exact: 1 Wb = 10⁸ maxwells. For context on related field units, see tesla and related units.

History and naming

The weber was named after Wilhelm Eduard Weber, a 19th‑century German physicist who contributed to early studies of electricity and magnetism. The adoption of the name and symbol into international usage followed the development and standardization of SI derived units in the 20th century. For biographical background, consult Wilhelm E. Weber sources.

Uses and practical examples

• Electrical engineering: flux linkage in transformers and inductors is expressed in webers to compute induced voltages.
• Magnetic circuit design: total flux through core cross sections is given in webers when sizing core and windings.
• Measurement and instrumentation: magnetometers and fluxmeters report integrated flux in webers for calibration and testing.

Applications range from power generation and electric motors to medical imaging devices and scientific instrumentation. For further technical resources and standards, consult relevant references.

Distinctions and common confusions

It is important to distinguish magnetic flux (measured in webers) from magnetic flux density or magnetic field strength (measured in teslas). Flux is an integrated quantity over an area, whereas flux density describes the field per unit area. Another potential confusion is between the symbol Wb and other unit symbols; Wb uniquely denotes the weber in SI notation.