Magnetic Flux, Flux Density and Remanence: What Is the Difference?

These terms all relate to magnetism, but describe different aspects of it.

Magnetic flux (Φ): Imagine the magnetic field as invisible lines that leave a north pole and loop back towards a south pole. Magnetic flux describes the total field passing through a particular surface. In a simple water-flow analogy, it resembles the total amount of flow passing through a pipe's cross-section. It is measured in webers (Wb).

Magnetic flux density (B): This describes magnetic flux per unit area for a uniform field perpendicular to that area. It indicates how densely packed the imaginary field lines are. Unlike water pressure, it is a field quantity per unit area. Magnetic flux density is measured in teslas (T), where 1 T = 1 Wb/m².

Residual flux density (Br): This is a property of certain magnetic materials, including permanent magnets. It is the flux density remaining after the external magnetising field is removed under the specified measurement conditions. It describes the magnetisation the material retains after magnetising. Remanence is also measured in teslas (T).

A simple analogy:

Imagine a crowd at a concert as an illustration of a magnetic field.

Magnetic flux (Φ) is analogous to the total number of people passing through a particular gate or area.

Magnetic flux density (B) is analogous to how closely packed the people are at that gate, expressed as the number per square metre.

Residual flux density (Br) can be compared loosely with the crowd density that remains after the main event has ended. The analogy is only illustrative; remanence is a property of the magnetic material.