MAGNETIC CIRCUITS
Electrical current flowing along a wire creates a magnetic field
around the wire, as shown in Fig. That magnetic field can be
visualized by showing lines of magnetic flux, which are represented
with the symbol φ.
The direction of that field that can be determined using the “right
hand rule”
,• Faraday discovered is that current flowing through the
coil not only creates a magnetic field in the iron, it also
creates a voltage across the coil that is proportional to
the rate of change of magnetic flux φ in the iron.
• That voltage is called an electromotive force, or emf, and
is designated by the symbol e.
Faraday’s law of electromagnetic
induction:
• The sign of the induced emf is always in a direction
that opposes the current that created it, a phenomenon
referred to as Lenz’s law.
,• In the magnetic circuit of Fig, the driving force, analogous to
voltage, is called the magneto motive force (mmf), designated
by F. The magneto motive force is created by wrapping N
turns of wire, carrying current i
Magneto motive force (mmf ) F = Ni (ampere − turns)
, • The magnetic flux is proportional to the mmf driving force
and inversely proportional to a quantity called reluctance R,
which is analogous to electrical resistance,
• resulting in the “Ohm’s law” of magnetic circuits given by
Electrical current flowing along a wire creates a magnetic field
around the wire, as shown in Fig. That magnetic field can be
visualized by showing lines of magnetic flux, which are represented
with the symbol φ.
The direction of that field that can be determined using the “right
hand rule”
,• Faraday discovered is that current flowing through the
coil not only creates a magnetic field in the iron, it also
creates a voltage across the coil that is proportional to
the rate of change of magnetic flux φ in the iron.
• That voltage is called an electromotive force, or emf, and
is designated by the symbol e.
Faraday’s law of electromagnetic
induction:
• The sign of the induced emf is always in a direction
that opposes the current that created it, a phenomenon
referred to as Lenz’s law.
,• In the magnetic circuit of Fig, the driving force, analogous to
voltage, is called the magneto motive force (mmf), designated
by F. The magneto motive force is created by wrapping N
turns of wire, carrying current i
Magneto motive force (mmf ) F = Ni (ampere − turns)
, • The magnetic flux is proportional to the mmf driving force
and inversely proportional to a quantity called reluctance R,
which is analogous to electrical resistance,
• resulting in the “Ohm’s law” of magnetic circuits given by
