Flux surface surrounding a charge "q" is "q"/ε. In free space the electric displacement is given by the constitutive relation D = ε E, so for any bounding surface the D-field flux equals the charge "Q" within it. Here the expression "flux of" indicates a mathematical operation and, as can be seen, the result is not necessarily a "flow", since nothing actually flows along electric field lines. The magnetic flux density (magnetic field) having the unit Wb/m (Tesla) is denoted by B, and magnetic flux is defined analogously: with the same notation above. The quantity arises in Faraday's law of induction,
Maxwell (unit) to measure. The "maxwell" was affirmed again unanimously as the unit name for magnetic flux at the Plenary Meeting of the International Electrotechnical Commission in July 1930 at Oslo. In 1933, the Electric and Magnetic Magnitudes and Units committee of the International Electrotechnical Commission recommended to adopt the metre-kilogram-second (MKS) system (Giorgi system), and the name weber was proposed for the practical unit of magnetic flux (), subject to approval of various national committees, which was achieved in 1935. The "weber" was thus adopted as a practical unit of magnetic flux by the International Electrotechnical Commission. The "maxwell" is a