A field of force that exists around a magnetic body (see magnetism) or a current-carrying conductor. Within a magnetic field a magnetic dipole may experience a torque and a moving charge may experience a force. The strength and direction of the field can be given in terms of the magnetic flux density (or magnetic induction), symbol B; it can also be given in terms of the magnetic field strength (magnetizing force or magnetic intensity), symbol H.
The magnetic flux density is a vector quantity and is the magnetic flux per unit area of a magnetic field at right angles to the magnetic force. It can be defined in terms of the effects the field has, for example by B=F/qvsinθ, where F is the force a moving charge q would experience if it was travelling at a velocity v in a direction making an angle θ with that of the field. The SI unit is the tesla.
The magnetic field strength is also a vector quantity and is related to B by:
where μ is the permeability of the medium. The SI unit of field strength is the ampere per metre (A m−1).