16 Analogue Recording and Reproduction
Magnetomotive force, m.m.f is given by
m.m.f. = NI
where N is the number of coil turns and I is the current.
The units of m.m.f are ampere turns/meter (At/m)
The intensity or field strength is the total force acting per unit length I of the magnetic circuit. It is called the magnetizing force H.
H = m.m.f./l = NI/l(AT/m)
The magnetizing force causes a flux Ф in the magnetic circuit.
The flux density B is the flux per unit area. The unit is the tesla (= webers/m2).
Ф = m.m.f./S
where S is the reluctance of the circuit.
Figure 73 shows a typical BH loop (hysteresis loop).