PPT: Magnetic Circuits | Basic Electrical Technology - Electrical Engineering (EE) PDF Download

 Page 1


  
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 f. 
The direction of that field that can be determined 
using the “right hand rule”
Page 2


  
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 f. 
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 f 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.
Page 3


  
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 f. 
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 f 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)
Page 4


  
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 f. 
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 f 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
Page 5


  
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 f. 
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 f 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
  
Magnetic field intensity (H):
With N turns of wire carrying current i, 
the mmf created in the circuit is Ni ampere-turns. With l 
 representing the mean path length for the magnetic 
flux, the magnetic field intensity is