Page 632 - Mechatronics with Experiments

618 MECHATRONICS
Coil 1 Coil 2 Coil

Soft iron

0
AC
Ampermeter
Galvanometer
(a) (b)

v - speed
x
Coil

S N
R
i B l

0

Galvanometer
Conductor
(c) (d)
FIGURE 8.9: Faraday’s law of induction: change in magnetic flux induces an opposing voltage
in an electrical circuit affected by the field. The induced voltage is proportional to the time rate
of change in the magnetic flux and in opposite direction to it. The source of the chance in
magnetic flux can be (a) a changing current source which generates the electromagnetic field,
(b) it can be due to the change in reluctance in a magnetic field (in other words, the inductance
of the electrical circuit changes). In inductive circuits, the back EMF can be due to
self-inductance itself and due to the change in the inductance), or (c) due to mechanical motion.
The last two cases are observed as back EMF on solenoids and DC motors, respectively. The
first case is observed in transformers. (d) Generator action as a result of Faraday’s law of
induction.

In electromagnetism, the current is the “cause” (source) and the magnetic field is the
“effect” of it. Faraday’s induction law states that the time rate of change in magnetic flux
induces EMF voltage on a circuit affected by it. The source of electromagnetic induction
(induced voltage) is the change in the magnetic flux. This change may be caused by the
following sources (Figure 8.9):

1. A changing magnetic flux itself, that is changing magnetic flux created by a changing
source current. In the case of a transformer, the AC current in the primary winding
creates a changing magnetic flux. The flux is guided by the iron core of the transformer
to the secondary winding. The changing magnetic flux induces a voltage in the
secondary winding (Figure 8.9a, Figure 8.11).