Magnetic fields, commonly denoted B, are caused by currents, or equivalently by the movement of charges. In particular, the fourth of the Maxwell equations (in cgs) gives
where c is the speed of light and J is the current density. The magnetic field due to a current loop of given configuration can be calculated directly from the Biot-Savart law in cgs as
where I is the current, a differential length element, and r the position vector, and in MKS as
where is the permeability of free space.
Biot-Savart Law, Electric Field, Electromagnetic Field, Electromagnetic Field Tensor, Lenz's Law, Magnetic Field Energy Density, Magnetic Flux, Magnetic Force, Maxwell Equations
References
Griffiths, D. J. Introduction to Electrodynamics, 3rd ed. Englewood Cliffs, NJ: Prentice-Hall, 1998.
Knoepfel, H. E. Magnetic Fields: A comprehensive Theoretical Treatise for Practical Use. New York: Wiley, 2000.
