A magnetic field can be produced by either a current, a flow of charged particles or a magnetised material. The pole of a magnet, a current-carrying wire or a moving charged particle in a magnetic field will feel a magnetic force.
The strength of the magnetic field at a point in space is called the magnetic flux density B and is measured in tesla (T). In electric fields we take the field's direction to be the direction of the force on a positive charge. Similarly, the direction of the magnetic flux density is the direction of the force on an isolated North pole.
The magnitude of the force on a wire carrying current I with length L in a magnetic field is given by the equation
F = ILB sinθ
where θ is the angle between the wire and the magnetic field. The force is perpendicular to the field and the current. The equivalent formula for the force on a moving charged particle of charge q and velocity v is F = qvB sinθ with the force perpendicular to field and velocity.