This document provides a lecture on electrical machines covering magnetics and magnetic circuits. It discusses the history of magnetism and defines different types of magnets including permanent magnets and electromagnets. It describes magnetic fields and flux, and important magnetic concepts such as flux density, magnetomotive force, magnetic field intensity, permeability, hysteresis, and B-H curves. It discusses the magnetic properties and behaviors of different materials including diamagnetic, paramagnetic, and ferromagnetic. Key terms are defined and examples are provided to illustrate various magnetic principles.

1. 12/15/2023 1
ADDIS ABABA SCIENCE AND TECHNOLOGY UNIVERSITY
COLLAGE ENGINEERING
DEPARTMENT OF ELECTRICALAND COMPUTER ENGINEERING
LECTURE ON ELECTRICAL MACHINE
(EMEg 3104)
2-0-3
Addis Ababa/Ethiopia
First semester 2023

2. Chapter one
Magnetics
Introduction to Magnetism and Magnetic circuit
The study of magnetism begin in the 13th century with many
famous scientists and physicists such as William Gilbert,
Christian Oersted, Michael Faraday, James Maxwell, Ampere and
Wilhelm Weber all having some input on the subject since.
Certain materials found in nature exhibit a tendency to attract
or repeal each other. These materials, called magnets.
A magnet:- is a material which has the property of attracting
small bits of iron and setting it self in a N-S direction when
suspended freely.
The name Magnet is taken from that of the ancient town magnet
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3. Cont…
Magnets are generally classified in two categories
 Permanent magnets
 Electro-magnets
Permanent magnets
is a piece of ferromagnetic material (such as iron, nickel or
cobalt) which has properties of attracting other pieces of
these materials.
They retain their magnetism indefinitely and no need of
electrical energy
A permanent magnet will position itself in a N & S direction
when freely suspended.
The north-seeking end of the magnet is called the N-Pole,
and the south-seeking end is the S-pole.
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4. Con’t
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Figure: 1.1 Permanent Magnet

5. Electro-magnets
Is the magnetization due to and only for flow of an
electric current through the coil.
Electro-magnet are also called artificial Magnet.
When an electric current flows through a
conductor, a magnetic field is produced.
The magnetic field produced in a conductor is
relatively weak and is proportional to the current
flowing through the conductor and the number of
turns wound on the materials
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6. Cont…
The higher the current flow, the stronger the
magnetic field produced.
The strength of magnetic field isn’t infinite and we
reach point of saturation where an increase in
current produces no further magnetic flux.
Winding a conductor into a coil will greatly
increase the magnetic field.
i.e the more turns of wire produces a stronger
magnetic field with out increase in current.
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7. 1.1. Magnetic flux (magnetic line of force)
Is the total magnetic lines of force produced by a
magnet
All electromagnetic devices make use of magnetic
fields in their operation.
Magnetic fields may be produced by permanent
magnets or electromagnets.
Magnetic fields are created by alternating- and direct-
current sources to provide the necessary medium for
developing generator action and motor action.
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IMPORTANT TERMS IN MAGNETICs

8. Cont.…
 The "quantity of magnetism" which exists in a
magnetic field is the magnetic line of force, or
more simply, the magnetic flux.
 In the SI system magnetic flux is measured in units
called webers, abbreviated Wb, and its symbol is 
( (the Greek lowercase letter phi).
 Although there is no actual flow of magnetic flux,
we will consider flux to be analogous to current in
electric circuits.
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9. What is a Magnetic field of a magnet?
 Magnetic field is the area around a magnet
In this area the effects of the magnetic force
produced by the magnet can be detected.
A magnetic field cannot be seen, felt, smelt or
heard and therefore it is difficult to represent.
Michael Faraday suggested that the magnetic field
could be represented pictorially, by imagining the
field lines of Magnetic flux which enables
investigation of the distribution and density of the
field to be carried out.
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10. Properties of magnetic lines
The direction of magnetic lines of flux radiates
from N-Pole to S-Pole outside the magnet and from
S-pole to N-Pole inside the magnet.
They always form complete closed paths
 They never intersect and always have a definite
direction.
 The laws of magnetic attraction and repulsion can
be demonstrated by using two bar magnets.
Unlike poles attract each other and like poles repel
each other. This is indicated in the fig 1.2 below.
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11. Properties of Magnetic Lines of Force
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Figure 1.2

12. Electromagnetism
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Figure 1.3
Electromagnetism is produced when an electrical current
flows through a simple conductor such as a piece of cable.
 The magnetic polarity in electro-magnet is dependent on
the direction of current flow.
 A magnetic field is always associated
with a current-carrying conductor.
 The magnetic field is strongest
perpendicular to the current direction
as shown in figure 1.3.

13. 1.2. Magnetic Flux Density
 Is the amount of magnetic flux per unit cross-
sectional area.
 The total magnetic flux that comes out of the
magnet is not uniformly distributed.
The magnetic flux density increases as we
approach closer to the end of the magnet
A greater amount of magnetic flux passing through
an area near to the pole of a magnet
 In other words, the magnetic flux density increases
as we approach closer to the end of the magnet.
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14. Cont.…
 However, it must be noted that the magnetic flux density
inside the magnet is uniformly constant.
 Magnetic flux density is measured in units of tesla (T) and
is given the symbol B.
 One tesla is equal to 1 weber of magnetic flux per square
meter of area. We can state that.
B= /A ………………………….1.
Where
B = magnetic flux density, T
 = magnetic flux, Wb
A = area through which  penetrates perpendicularly, m2
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15. Example
The total magnetic flux out of a cylindrical permanent
magnet is found to be 0.032 mWb. If the magnet has a
circular cross section and a diameter of 1 cm.
what is the magnetic flux density at the end of the
magnet?
Solution???
As we move away from the end of the magnet, the
magnetic flux spreads out, and therefore the magnetic
flux density decreases.
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16. 1.3. Magneto motive Force
 Magnetomotive Force is a driving force causing to establish
magnetic flux.
 An increase in the magnitude of current in a coil or a single
conductor results in an increase in the magnetic flux.
 If the number of turns in a coil are increased (with the
current remaining constant), there is an increase in
magnetic flux.
 Therefore, the magnetic flux is proportional to the products
of amperes and turns.
 This ability of a coil to produce magnetic flux is called the
Magnetomotive force.
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17. Example
#2. The coil below has 1000 turns wound on a cardboard toroid.
The diameter D of the toroid is 10 cm, and the cross section is 1 cm.
The total magnetic flux in the toroid is 3Wb when there is an
excitation current of 10 mA in the coil.
a) What is the magnetic flux when the current is increased to 20
mA?
b) What is the magnetic flux density within the coil when the current
is 20 mA
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18. 1.5. Magnetic Field Intensity
 Also known as Magnetizing force or magnetic
field strength.
 It is the magneto motive force gradient per unit
length of magnetic circuit and represented by H.
 The unit is ampere-turns per meter (At/m).
 The former name for magnetic field intensity was
magnetizing force.
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19. 1.6. Permeability
Permeability (μ) – the magnetic property of a material to
allow itself to be magnetized.
It determines the characteristics of magnetic materials and
nonmagnetic materials.
Permeability of a material means its conductivity for
magnetic flux
The grater the Permeability, the greater is its conductivity for
magnetic flux
The reluctance of magnetic materials is much lower than
that of air or nonmagnetic material.
The permeability of magnetic materials is much greater than
that of air or non magnetic material
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20. Con’t
Where r is the relative permeability, and is defined as
r varies with the type of magnetic materials and, since it
is the ratio of flux densities, it has no unit.
From its definition, r for a vacuum is 1.
 0 r =  , is called absolute or actual permeability of
materials
o- actual permeability of air or non magnetic materials
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21. Example
Calculate the absolute and relative permeabilities of cast steel operating
at magnetic flux densities of 0.7 T and 1.0 T if the values of
magnetizing force are 400At/m and 800 At/m respectively
Solution
The absolute permeabilities are:
 For 0.7T :??
 For 1 T:??
The Relative permeability's are:
 For 0.7 T :??
 For 1 T : ??
 Cast steel has at least 1000 times more ability to set up magnetic
flux lines than nonmagnetic materials
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22. Magnetic properties of Materials
Magnetic materials can be classified as
a)Diamagnetic
b)Para magnetic
c)Ferromagnetic
Diamagnetic Materials
Those substances that experience a feeble or very weak
force of repulsion are called diamagnetic materials, such
as bismuth, silver, Methane, water and copper.
The permeability of a diamagnetic material is slightly less
than the permeability of free space.
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23. Cont.…
Paramagnetic Materials
Those substances that experience a feeble force of repulsion
are called Paramagnetic materials but the permeability is
slightly greater than the permeability of free space.
Example: Air, Aluminum, oxygen, Manganese, platinum and
palladium
Since the force experienced by a paramagnetic or a
diamagnetic substance is quite feeble and their permeability
differ slightly from that of free space, for all practical
purposes we can group them together and refer to them as
nonmagnetic materials.
These materials are of no practical use in the construction of
magnetic circuits.
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24. Ferromagnetic materials
The permeability of these materials are greater than
free space.
The principal ferromagnetic material is Iron,
nickel various steel and alloys
The magnetic force of attraction experienced by a
ferromagnetic material may be 5000 times that
experienced by a paramagnetic material.
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25. Magnetization (B-H) Curve
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The nonlinear relationship between magnetic flux density and
magnetic field intensity
It indicates the manner in which the B varies with H
By plotting measured values of flux density B against magnetic field
intensity H, a magnetization (B–H) curve is produced.
Typical magnetization or B-H curves for sheet steel, cast iron, and air
are plotted in Figure 1.4.
Fig. 1.4

26. Cont.…
It is observed that the magnetic flux density (B) increases
almost linearly with an increase in the magnetic field
intensity (H) up to the knee
Beyond the knee a continued increase in H results in a
relatively small increase in B
 When ferromagnetic materials experience only a slight
increase in flux density for a relatively large increase in
magnetic field intensity, the materials are said to be
saturated.
 Magnetic saturation occurs beyond the knee of the
magnetization curve.
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27. Cont…
The characteristic of saturation is present only in
ferromagnetic materials.
An explanation of magnetic saturation is based on
the theory that magnetic materials are composed
of very many tiny magnets (magnetic domains)
that are randomly positioned when the material is
totally demagnetized.
Upon application of a magnetizing force (H), the
tiny magnets will tend to align themselves in the
direction of this force
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28. Cont.…
 In the lower part of the magnetizing curve, the
alignment of the randomly positioned tiny magnets
increases proportionately to the magnetic field
intensity until the knee of the curve is reached.
 Beyond the knee of the curve, fewer tiny magnets
remain to be aligned, and therefore large increases
in the magnetic field intensity result in only small
increases in magnetic flux density.
 When there are no more tiny magnets to be
aligned, the ferromagnetic material is completely
saturated.
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29. Cont.…
 In the saturation region of the curve, the magnetic
flux density increases linearly with magnetic field
intensity, just as it does for free space or
nonmagnetic materials.
 From the origin of the B-H curve there is a slight
concave curvature beyond which is the essentially
linear region.
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30. Cont.…
The r of a ferromagnetic material is proportional to
the slope of the B–H curve and thus varies with the
magnetic field strength.
The approximate ranges of values of μr for some
common magnetic materials are indicated in table
below
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31. Hysteresis
 Hysteresis is the name given to the "lagging" of
flux density B behind the magnetizing force H.
 Hysteresis loop is obtained, when a ferromagnetic
material is taken one cycle of magnetization.
If a ferromagnetic material has been completely
demagnetized (H = B= 0) and the magnetizing
force H is increased in steps from zero, the
relationship between flux density B and H is
represented by the curve oab in figure below
which is the normal magnetization curve.
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32. Cont.…
At a particular value of H, shown as Oy, it becomes
difficult to increase the flux density any further. The
material is said to be saturated.
Thus by is the saturation flux density.
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Figure 1.5

33. Cont…
 If the value of H is now reduced it is found that the flux
density follows curve bc.
 When H = zero, B is not, but has a definite value B= oc
Removing H, the iron bar is not completely demagnetized.
 This value of oc is called remanence or residual flux
density (Br).
 To demagnetize the iron bar, we have to apply the H, in
the reverse direction.
 When H is increased in the opposite direction (by
reversing current in the solenoid), B has been reduced to
zero at point d, where H= od.
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34. Con’t
 The value of H shown by Od required to remove the
residual magnetism, i.e. reduce B to zero, is called the
coercive force (Hc).
 Further increase of H in the reverse direction causes the
flux density to increase in the reverse direction until
saturation is reached, as shown by curve de.
 If H is varied backwards from Ox to Oy, the flux density
follows the curve efgb, similar to curve bcde.
The closed figure bcdefgb is called the hysteresis loop (or
the B/H loop).
Hysteresis loop is obtained when an iron bar is taken one
complete cycle of magnetization
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35. Hysteresis Loss
When a ferromagnetic material subjected to a cycle
of magnetization, molecular friction or disturbance
in the alignment of domains (i.e. groups of atoms)
takes place in the material and causes energy to be
expended.
This energy appears as heat in the specimen and is
called hysteresis loss.
Hysteresis loss is proportional to the area of the
hysteresis loop
The shape and area of the hysteresis loop will
depend upon the nature of magnetic material.
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36. Cont…
The area, and thus the energy loss, is much greater
for hard materials than for soft materials.
The effect of Hysteresis loss is the rise of
temperature of the machine
Figure below Shows typical hysteresis loops for:
a)hard material, which has a high remanence oc and
a large coercivity od
b)soft steel, which has a large remanence and small
coercivity,
c)ferrite, this being a ceramic-like magnetic
substance made from oxides of iron, nickel, cobalt,
magnesium, aluminum and manganese; the
hysteresis of ferrite is very small.
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37. Con’t
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Soft material is used in the construction of
transformer, IM and Synchronous machine (Small
area, Low hysteresis loss)
Hard material is used in the construction of
permanent magnet. (Large area, High hysteresis loss)
Figure 1.6 Hysteresis Loop of different Material

38. Conclusion
 Hysteresis in magnetic materials results in dissipation of
energy, which is proportional to the area of the hysteresis
loop.
Hence the following conclusions can be drawn:
Flux density B always lags with respect to the
magnetizing force H.
An expenditure of energy is essential to carry the
specimen through a complete cycle of magnetization.
Energy loss is proportional to the area of hysteresis
loop and depends upon the quality of the magnetic
material.
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39. Why does hysteresis occur?
To understand hysteresis in a ferromagnetic core, we have
to look the behavior of its atomic structure before, during
and after the presence of a magnetic field.
The atoms of iron and similar metals (cobalt and nickel)
tend to have their magnetic fields closely aligned with
each other.
Within the metal, there is a small regions known as
domains where in each domain there is a small magnetic
field which randomly aligned through the metal structure
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40.  An example of a magnetic domain orientation in a metal
structure before the presence of a magnetic field
Magnetic field direction in each domain is random such
that the net magnetic field is zero.
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41. Cont…
When m.m.f is applied to the core, each magnetic
field will align with respect to the direction of the
magnetic field.
That explains the exponential increase of magnetic
flux during the early stage of magnetization.
As more and more domain are aligned to the
magnetic field, the total magnetic flux will
maintain at a constant level and is said to be
saturation.
When m.m.f is removed, the magnetic field in each
domain will try to revert to its random state.
12/15/2023 41

42. Eddy Current Loss
A time-varying flux induces voltage within a ferromagnetic core.
These voltages cause flow of current within the core and
which is called eddy currents.
Energy is dissipated (in the form of heat) because these eddy
currents are flowing in a resistive material (iron).
The amount of energy lost due to eddy currents is
proportional to the size of the paths they follow with in the
core.
To reduce energy loss, ferromagnetic core should be broken
into small strips, or laminations, and build the core from
these strips.
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43. Cont…
An insulating oxide or resin is used between the
strips, so that the current paths for eddy currents
are limited to small areas.
12/15/2023 43
Figure 1.7

44. MAGNETIC CIRCUITS
 A toroid of homogeneous magnetic material, such
as iron or steel, is wound with a fixed number of
turns of insulated wire as shown in Figure 1.8.
 The magnetic flux () and the excitation current
(I) are related by:
12/15/2023 44
Figure 1.8

45. Comparison between Electrical and
Magnetic Circuit
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46. Cont.…
 We can draw useful electrical analogs for the
solution of magnetic circuit problems.
 In an electrical circuit the driving force is the
voltage, the output is the current, and the
opposition to establishing current is the resistance.
 In the same way, the driving force in the magnetic
circuit is the magnetomotive force, the output is
the magnetic flux, and opposition to establishing
the flux is the reluctance.
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47. Series and Parallel Magnet Circuits
 By definition, a series magnetic circuit contains
magnetic flux, which is common throughout the
series magnetic elements.
 These series magnetic elements may consist of
composite sectors of ferromagnetic materials of
different lengths and cross-sectional areas, and of air
gaps.
 The simplest series magnetic circuit would be of a
toroid of homogeneous material and the steel core of
a transformer.
 More complex series circuits which contain air gaps .
12/15/2023 47

48. Series Magnet Circuit
 For the magnetic circuit of Figure 1.9a the analogous electric
circuit and the analogous magnetic circuit are in Figure 1.9b
and c, respectively.
 The iron and air portions of the magnetic circuit are
analogous to the two series resistors of the electric circuit.
 Analogous to the electric circuit, the magneto-motive force
must overcome the magnetic potential drops of the two series
reluctances in accordance with Kirchhoff's voltage law
applied to magnetic circuits.
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is the equivalent magnetic-potential-drop equation

49. Cont.…
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 Hence we can calculate the MMF drop for the iron as follows:
l is length
Figure 1.9 Iron Core toroid with air gap

50. Cont.…
 Finally, the general MMF-drop equation for series
magnetic circuits is modified for calculation purposes to
the following form:
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 In analogous equivalents, Kirchhoff's current law for
magnetic circuits states that the sum of magnetic fluxes
entering a junction or node is equal to the sum of
magnetic fluxes leaving the junction or node.

51. Parallel Magnetic Circuit
 Figure 1.10a shows a parallel magnetic circuit.
 There are NI ampere-turns on the center leg .
 The flux that is produced by the MMF in the center leg
exists and then divides into two parts, one going in the
path afe and the other in the path bcd.
 If we assume for simplicity that afe = bcd, the flux is
distributed evenly between the two paths. Now
g = afe + bcd
Where g = flux in portion g
afe = flux in portion afe
bcd = flux in portion bcd
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52. Cont.…
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Figure 1.10 Magnetic circuit with center leg

53. Cont.…
 Equation (*) is actually the analog of Kirchhoff's current
law, but now we can say that the amount of flux entering a
junction is equal to the amount of flux leaving the
junction.
 Another observation that we may make on this circuit is
that the MMF drops around a circuit are the same no
matter what path we take.
 Thus the MMF drop around afe must be equal to the MMF
drop around bcd.
 This can be stated more precisely as
Hala + Hflf + Hele = Hblb + Hclc + Hdld ….. Eq(*)
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54. Cont.…
 The drop in MMF around either path afe or bcd must
also be equal to the MMF drop along path g.
 But g also has an "active source," the NI ampere-turns
of the coil.
 The actual MMF existing between X and Y is the
driving force NI minus the drop Hglg in path g. Then
we can write
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55. Cont.…
12/15/2023 55
and in Figure 1.l3c we may write
E - RgIg = Ibcd (Rb + Rc + Rd )
= Iafe (Ra + Rf + Re )
Again we can draw analogous magnetic and electrical
circuits as in Figure 1.13b and c. For Figure 1.l3b we may
write

56. Electromagnetic Induction
 An electromagnet is made from a coil of wire which acts
as a magnet when an electric current passes through it.
 Often an electromagnet is wrapped around a core of
ferromagnetic material like steel, which enhances the
magnetic field produced by the coil.
 Oersted in 1820 discovered a very important phenomenon
giving the relationship between magnetism and
electricity.
 As per this relationship, a conductor carrying a current I is
surrounded all along its length by a magnetic field, the
lines of magnetic flux being concentric circles in planes at
right angles to the conductor
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57. Cont.…
 From his experiments, Faraday concluded that a current
was generated in a coil so long as the lines of force
bearing through the conductor changed.
 The current thus generated is called the induced current
and the emf that gives rise to this induced current is
called the induced emf.
 This phenomenon of generating an induced current in a
closed circuit by changing the magnetic field through it,
is called electromagnetic induction.
 The operation of electrical equipment like motors,
generators, transformers, etc. is mainly based upon the
laws formulated by Faraday.
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58. Faraday’s law
 Faraday's first law states that whenever the magnetic
flux associated or linked with a closed circuit is
changed, or alternatively, when a conductor cuts or is
cut by the magnetic flux, an emf is induced in the circuit
resulting in an induced current.
 This emf is induced so long as the magnetic flux changes.
 Faraday's second law states that the magnitude of the
induced emf generated in a coil is directly proportional to
the rate of change of magnetic flux.
 These two basic laws discovered by Faraday changed the
course of electrical engineering and led to the
development of generators, transformers, etc.
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59. Faraday’s Laws Of Electromagnetic Induction
First law:- Whenever the magnetic flux linking a coil changes,
an e.m.f is induced in it or whenever conductor cuts magnetic
flux an e.m.f is induced in that conductor.
Second law:- the magnitude of induced e.m.f in a coil or circuit
is equal to the rate of change of flux linkage.
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If there is N number of turns in the coil with the same flux
flowing through it, hence
Note that negative sign is in accordance to lenz’Law, which
states that the induced voltage in the coil produce a current that
would cause a flux opposing the original flux change.

60. Production of EMF
When an electric current flow through a conductor a
magnetic field is produced around the conductor.
 As a result an emf is induced in a conductor which is
cut by magnetic flux is known to be electromagnetic
induction.
 The change of flux as discussed in the Faraday's laws
can be produced in two different ways:
(i) by the motion of the conductor or the coil in a
magnetic field, i.e. the magnetic field is stationary and
the moving conductors cut across it.
 The emf generated in this way is normally called
dynamically induced emf;
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61. Cont.…
(ii) by changing the current (either increasing or
decreasing) in a circuit. thereby changing the flux
linked with stationary conductors, i.e. the conductors
or coils remain stationary and the flux linking these
conductors is changed.
 The emf is termed statically induced emf.
 Statically induced emf can be further subdivided
into
(a) self-induced emf and
(b) mutually induced emf.
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62. Cont.…
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 Consider a coil of N turns carrying a current of I
amperes and let Φ be the resulting flux linking the
coil.
 The magnetic flux forms complete loops as shown
in Fig. above
 Now if the current flowing in the coil is changed,
then the number of lines linking the coil also
changes.
 As such emf is induced in the coil according to
Faraday's laws of electromagnetic induction.
 This emf is termed as the emf of self-induction.

63. Mutually Induced emf
 The phenomenon of generation of induced emf in a circuit by
changing the current in a neighboring circuit is called mutual
induction.
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 Consider two coils P and S such that P is connected to a
battery through switch K and S to a galvanometer as
shown in fig. above.
When switch K is closed suddenly to start current in coil
P, the galvanometer gives a sudden "kick" in one
direction.
Now when K is opened, the galvanometer again shows a
deflection but in the opposite direction.

64. Production of Induced Force on a Wire
1. A current carrying conductor present in a uniform
magnetic field of flux density B would produce a
force to the conductor.
 If the conductor is perpendicular to the direction of
the magnetic field. the force induced is given by:
F = i (l × B)
Where: i – Current flow in the conductor
l – Length of the wire
B – Magnetic field density
12/15/2023 64

65. Cont…
2. If the current carrying conductor is positioned at
an angle to the magnetic field, the force is given by:
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Where: θ - angle between the conductor and the
direction of the magnetic field
3. The direction of the force depends on the direction
of current flow and the surrounding magnetic field.
The direction of the force is given by Fleming’s
right-hand rule.

66. Cont…
 A rule of thumb to determine the direction can be
found using the right-hand rule as shown below:
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4. In summary, this phenomenon is the bases for an
electric motor where torque or rotational force of
the motor is the effect of stator and rotor magnetic
fields.

67. Induced Voltage on a Conductor Moving in a
Magnetic Field
1. If a conductor moves or ‘cuts’ through a magnetic field,
Voltage will be induced between the terminals of the
conductor
The magnitude of the induced voltage is dependent upon
the velocity of the conductor assuming that the magnetic
field is constant.
This can be summarized in terms of formulation as shown:
Ein=(VXB) l
Where: V – velocity of the wire
B – magnetic field density
l – length of the conductor in the magnetic field
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68. Con’t…
2. Note: The value of (length) is dependent upon the
angle at which the wire cuts through the magnetic field.
Hence a more complete formula will be as follows:
Ein=(VXB)l cos θ
Where: θ - angle between the conductor and the direction
of (v x B)
3.The induction of voltages in a wire moving in a
magnetic field is fundamental to the operation of all
types of generators.
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69. Applications of Magnets
 Magnetism plays an important role in Electrical
and Electronic Engineering because components
such as relays, solenoids, inductors, loudspeakers,
motors, generators, transformers, circuit breakers,
televisions, computers, tape recorders, telephones
and electricity meters etc, would work if
magnetism exist.
 Then every coil of wire uses the effect of
electromagnetism when an electrical current flows
through it.
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