Electromagnetism is the branch of engineering dealing with the magnetic effects of an electric current. A conductor carrying a current is always surrounded along its length by a magnetic field. When a current-carrying straight conductor is placed in a magnetic field, it experiences a mechanical force whose magnitude depends on the flux density of the magnetic field, the current in the conductor, and the active length of the conductor in the magnetic field. Magnetomotive force in a magnetic circuit is produced by turns of a coil and current flowing through it, and is given by the product of the number of turns and current in amperes.

1. Chandrashekhar S Patil
Sharad Institute of Technology
Polytechnic
Yadrav
Unit 1.3.1-Electric and Magnetic
Circuits
(Electromagnetism, MMF)

2. Contents
Sr No. Topic Slide Number
01. Electromagnetism. 03
02. Magnetic field due to straight conductor. 05
03. Force on a current carrying conductor. 06
04. Flemings Left hand rule 07
05. Permeability 09
06. Absolute Permeability 10
07. Relative Permeability 11
08. Magneto motive Force(MMF) 12
2

3. Electromagnetism
A conductor carrying a current is always is surrounded all
along its length by a magnetic field. This important
relationship between the magnetism and current electricity
which was discovered by Oersted in 1920 forms the basis
of electromagnetism.
Important properties of magnet:-
 It attracts small pieces of iron.
 If suspended freely by a piece of silk fibre, it sets itself in
a definite direction so that its North pole points towards
North direction and South pole points towards South
direction.
 Like magnetic poles repel and unlike poles attract each
3
Electromagnetism is the branch of engineering dealing with the magnetic
effects of an electric current.

4. Definitions
4
Magnetic Induction:- It is the phenomenon due to which a magnet can
induce magnetism in a neighbouring piece of magnetic material (say iron)
without actual physical contact.
Pole Strength: The magnitude of the force exerted by one magnet on
another magnet gives an idea of pole strength.(Unit of pole strength is
Weber).
A line of force may be defined as a line along which an isolated N-pole
would travel if free to move in a magnetic field
Magnetic Flux:- The total number of lines of force in any particular
magnetic field is called the magnetic flux.
Magnetic Flux Density(B):-
The flux per unit area(a) in a
plane at right angles to the
flux is known as Flux
Density,Unit is Tesla.

5. Magnetic Field Due to straight conductor
5
A straight conductor carrying an
electric current is always
surrounded by all along its length
by a magnetic field.
The lines of force are in the form
of concentric circles in planes at
right angles to the conductor and
their direction is dependent on the
direction of current producing
them.
The right hand gripping rule:-
Grip the current carrying
conductor in the right hand with
the thumb outstretched parallel to
the conductor and pointing in the
direction of current.

6. Force on a current carrying conductor
It is observed that whenever a current carrying straight
conductor is placed in magnetic field it experiences a
mechanical force. The magnitude of this force is
dependent on the following factors.
(1) Flux density(B) of the magnetic field in which the
conductor is
placed(in tesla).
(2) Magnitude of the current(I) in the conductor(in
amperes).
(3) Active length(l) of the conductor (in meters).Active
length is the
part of the total length of the conductor which actually
lies in the
magnetic field.6

7. Flemings Left hand rule
Arrange the first finger, the second finger and the thumb of
your left hand mutually at right angles to one another Point
the first finger in the direction of the field and the second
finger in the direction of current
It will be interesting to know how this force is actually
produced Fig(a)
Shows a straight current carrying conductor in a direction
towards the observer and placed in a uniform magnetic7

8. 8
• The original field and that due to the conductor are also
shown in fig(a). These two fields combine to form a single
resultant field.
• It will be seen that in the region below the conductor, both
the fields act in the same direction and therefore give a
resultant field at any point equal to the sum of the individual
fields at that point.
• In the region above the conductor one field acts in the
direction opposite to that of the other and so the resultant is
the difference of the two fields.
• In general the original field of the magnet is strengthened at
the bottom of the conductor and weakened at the top. The
resultant pattern is shown in fig (b) In effect it seems that as
if some of the lines of force from the top region are
transferred to the bottom region.
• Due to crowding the lines of force in the lower region gets
stretched like a rubber band .Therefore they try to contract
and therby push the conductor upwards.Thus the conductor
experiences a mechanical force in the upward direction.

9. Permeability
9
Definition:-It may be defined as the ease of which a
magnetic flux permeates a medium or in other words or its
is the receptiveness of the medium in having flux set up in
it.
Permeability of free space or magnetic space constant
For a magnetic field in vacuum or(free space) the ratio of
flux density (in tesla)to magnetic field strength (in
amperes/meter) producing that flux density is called the
permeability of the free space or magnetic space constant.
It is the measure of the ease with which a magnetic flux
permeates(passes through) a vacuum.

10. Absolute Permeability(µ)
10
The ratio of magnetic flux density( in tesla) in a particular
medium(other than vacuum) to the magnetic field
strength(in amperes/meter) at the same location producing
that flux density is called the absolute permeability of that
medium
It is also taken as the measure of the ease with which a
magnetic flux permeates a medium or in other words, it is a
measure of the receptiveness of the medium to having flux
set p in it.The unit of absolute permeability(µ) is henry per
metre(H/m).

11. Relative Permeability
11
 The ratio of flux density produced in a material to the
flux density produced in a vacuum (or free space) by the
same magnetic field strength under identical conditions
is called the relative permeability of that material.

12. Magneto motive force(F)
12
In a electric circuit we know that electric current is due to
presence of electromotive force. Similarly in the magnetic
circuit it is due to the presence of magnetomotive force.
This magnetomotive force which produces or tends to
produce the flux in the magnetic circuit is given by the
product of turns on the magnetizing coil(N) and the current
flowing in the coil(I) amperes.
MMF= N * I amperes.

13. Thank you
13