Magnetic field Magnetic field is a force which is generated due to energy change in a volume of space. A magnetic field is produced by an electrical charge in motion e.g. current flowing in a conductor, orbital movement and spin of electrons. The magnetic field can be described by imaginary lines as shown in the figure below for a magnet and a current loop. Magnetic lines of force Current
Magnetic field Strength If a magnetic field, H, is generated by a cylindrical coil (solenoid) of n turns and length l, H = nI/l (A/m) Magnetic flux density, B: It is the magnitude of the field strength within a substance subjected to a field H B = H (Tesla or Weber/m2) , called the permeability, is the measure of the degree to which a material can be magnetized. In vacuum B = oH. o is the permeability of vacuum and is a universal constant. o = 4 x 10-7(H/m). r = /o is the relative permeability.
Magnetic moments Being a moving charge, electrons produce a small magnetic field having a magnetic moment along the axis of rotation. The spin of electrons also produces a magnetic moment along the spin axis. Magnetism in a material arises due to alignment of magnetic moments.