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INTRODUCTION TO MACHINERY PRINCIPLES
INTRODUCTION TO MACHINERY PRINCIPLES 2.7
FIGURE 2.3 B-H curves of selected soft magnetic materials.
Energy is lost in all iron cores due to the fact that energy is required to turn the domains.
The energy required to reorient the domains during each cycle of the alternating current is
called the hysteresis loss in the iron core. The area enclosed in the hysteresis loop is directly
proportional to the energy lost in a given ac cycle (Fig. 2.4).
FARADAY’S LAW—INDUCED VOLTAGE FROM A
MAGNETIC FIELD CHANGING WITH TIME
Faraday’s law states that if a flux passes through a turn of a coil of wire, a voltage will be
induced in the turn of wire that is directly proportional to the rate of change of the flux with
time. The equation is
d
e
ind dt
where e is the voltage induced in the turn of the coil and is the flux passing through it.
ind
If the coil has N turns and if a flux passes through them all, then the voltage induced
across the whole coil is
d
e
N
ind dt
where e voltage induced in coil
ind
N number of turns of wire in coil
flux passing through coil
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