16  Analogue Recording and Reproduction

Formulae

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).

image

Figure 73  Hysteresis loop ...

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