## magnetic induction

A vector field, usually denoted by

**B**, defined as follows.The torque Thus by measuring Magnetic induction is sometimes called magnetic field, a term usually applied to a different field where μ

**N**experienced by a magnetic dipole with magnetic dipole moment**m**is**N**for**m**oriented in two orthogonal directions, the magnetic induction components are obtained as torque components divided by the magnitude of**m**. The fundamental relation linking electric field**E**and magnetic induction**B**to the force on a charge*q*with velocity**v**is the Lorentz force equation**H**, related to**B**but different from it. In free space,**B**and**H**are proportional:_{0}, the permeability of free space, is a universal constant.**B**is the primitive field, whereas**H**is secondary, not strictly needed but convenient. Care must be exercised in deciding if, by magnetic field,**B**or**H**is meant. What is usually meant by the electric and magnetic fields (or the electromagnetic field) are**E**and**H**, although according to the Lorentz force equation**E**and**B**are the fundamental fields. Moreover, the Lorentz transformation preserves the (**E**,**B**) structure but not the (**E**,**H**) structure.