1. DISCOVER . LEARN . EMPOWER
INSTITUTE ENGINEERING
DEPARTMENT ACADEMIC UNIT-1
Bachelor of Engineering (Computer Science & Engineering)
Subject Name Basics Electrical & Electronics Engineering
Subject Code 22ELH-101
By
Navjeet kaur
Lecture No. 6
Introduction to Magnetic Circuit
2. 2
Lecture
Objectives
S. No. Objectives
1 To make student aware about the basic concept of magnetic circuit
2 To aware about importance of magnetic circuit
3 To provide knowledge about different terminologies of magnetic circuit
4 To make familiar with types of magnetic circuit.
5 To give brief knowledge about applications of magnetic circuit.
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electrical-theory/
3. 3
Course
Objectives
S. No. Objectives
1 To meet students with basic knowledge of dc circuits, electromagnetism and ac fundamentals.
2
To aware about introduction to single and three phase ac circuit with their construction and
working principles.
3 To provide knowledge about electrical and electronics engineering fundamentals.
4
To acquire specific knowledge skills so as to comprehend how electric, magnetic and electronic
circuits are applied in practice.
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electrical-theory/
4. 4
Course
Outcomes
CO
Numbe
r
Title Level
CO1
Identify the different types of electrical elements and the basic op-amp
circuit elements and to illustrate the various types of motors, transducers
and batteries.
Remember
CO2
Understand basic principles of transformers, transducers, op-amps, DC
and AC motors and to compare the different methods for analyzing
electrical and magnetic circuits.
Understand
CO3
Derive the relationships between parameters in electric and magnetic
circuits and motors and to determine specifications of op-amps.
Analyze
CO4
Solve the basic problems related to electric circuits, magnetic circuits and
motors and to assess the characteristics of different configurations of op-
amps.
Evaluate
CO5
Design the different applications of transducers, motors as well as the op-
amps like adders, subtractor and comparators. Create
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electrical-theory/
5. Content
Introduction to magnetic circuit
Terms used in magnetic circuit
Magnetic field and magnetic field lines
Concept of Magnetomotive force and magnetic flux
Concept of Magnetic field intensity and magnetic reluctance
Concept of Magnetic permeance and magnetic permeability
Faraday’s Laws
5
6. What is Magnetic Circuit?
• The closed path followed by magnetic lines of forces is called
the magnetic circuit.
• In the magnetic circuit, magnetic flux or magnetic lines of force
starts from a point and ends at the same point after completing its
path.
• Flux is generated by magnets, it can be a permanent magnet or
electromagnets.
• A magnetic circuit is made up of magnetic materials having high
permeability such as iron, soft steel, etc.
• Magnetic circuits are used in various devices like electric motor,
transformers, relays, generators galvanometer, etc.
6
8. Terms Used in Magnetic Circuit
• Magnetic field: Magnetic Field is the region around a magnetic
material or a moving electric charge within which the force of
magnetism acts.
• Magnetic Field Lines: The use of field lines is an alternative way to
represent the information contained within a magnetic vector field.
Magnetic field lines are imaginary lines.
• Magnetic field lines are a visual tool used to represent magnetic
fields. They describe the direction of the magnetic force on a north
monopole at any given position
8
9. Terms Used in Magnetic Circuit
• Magnetomotive Force (MMF): The current flowing in an electric
circuit is due to the existence of electoromotive
force similarly magnetomotive force (MMF) is required to drive
the magnetic flux in the magnetic circuit.
• The magnetic pressure, which sets up the magnetic flux in a magnetic
circuit is called Magnetomotive Force.
• The SI unit of MMF is Ampere-turn (AT), and their CGS unit is G (gilbert).
9
10. Terms Used in Magnetic Circuit
10
https://circuitglobe.com/what-is-magnetomotive-force.html
Fig. 2 Magnetic coil with N turns
11. Terms Used in Magnetic Circuit
• The MMF for the inductive coil shown in the figure below is expressed
as
• Where, N – numbers of turns of the inductive coil
I – current
• The strength of the MMF is equivalent to the product of the current
around the turns and the number of turns of the coil.
• As per work law, the MMF is defined as the work done in moving the
unit magnetic pole (1weber) once around the magnetic circuit.
11
…………………………..(1)
12. Terms Used in Magnetic Circuit
• The magnetomotive force can measure regarding magnetic field
intensity and the length of the substance.
• The magnetic field strength is the force act on the unit pole placed on
the magnetic field. MMF regarding field intensity is expressed as
• Where H is the magnetic field strength, and l is the length of the
substance.
12
……………………………….(2)
13. Terms Used in Magnetic Circuit
• Magnetic flux: The number of
magnetic lines of forces set up in a
magnetic circuit is called Magnetic
Flux.
• It is analogous to electric current, I in
an electric circuit. Its SI unit is Weber
(Wb)
• The fluxmeter has to measure coil
which measures the variation of
voltage to measure the flux.
13
http://www.schoolphysics.co.uk/age16-
19/Electricity%20and%20magnetism/Electroma
gnetism/text/Flux_and_flux_density/index.html
Fig. 3 Magnetic coil with N turns
14. Terms Used in Magnetic Circuit
• Net number of lines passing through the surface are called magnetic
lines of forces.
14
Fig. 4 Magnetic coil with lines of force
…………………………………(3)
15. Terms Used in Magnetic Circuit
If the magnetic field is constant than the magnetic flux passing through
a surface (S) is
where
B – the magnitude of the magnetic field
S – area of surface
θ – angle between the magnetic field lines and perpendicular
distance normal to the surface area
The unit of magnetic flux is weber.
15
…………………………..(4)
16. Terms Used in Magnetic Circuit
• Magnetic Field Intensity: The Magnetic Field Intensity or Magnetic
Field Strength is a ratio of the MMF needed to create a certain Flux
Density (B) within a particular material per unit length of that
material. H = At/m, ampere-turns per meter.
• N is used as the number of turns of wire around a core
or magnetic material. So the H = N*I/m.
16
17. Terms Used in Magnetic Circuit
17
https://www.coolmagnetman.com/magfund06.htm
Fig.5 Magnetic coil
18. Terms Used in Magnetic Circuit
• Let, l = mean length of the magnetic circuit
A = cross-sectional area of the core
µr = relative permeability of the core
Now the flux density in the core material
• Magnetising force in the core
18
………………………………..(1)
………………………………………………..(2)
………..(3)
19. Terms Used in Magnetic Circuit
• According to work law, the work done in moving a unit pole once
round the magnetic circuit is equal to the ampere-turns enclosed by
the magnetic circuit.
• It is measured in ampere-turn/meter.
19
……………………………….(4)
………………………...……(5)
20. Terms Used in Magnetic Circuit
• Magnetic Reluctance: The obstruction offered by a magnetic circuit
to the magnetic flux is known as reluctance.
• Reluctance in magnetic circuit stores the magnetic energy.
• Also in an electric circuit, the electric field provides the least
resistance path to the electric current.
• Similarly, the magnetic field causes the least reluctance path for the
magnetic flux. It is denoted by S.
20
21. Terms Used in Magnetic Circuit
• L- the length of the conductor
μo – permeability of vacuum which is equal to 4π Χ10^7 Henry/metre.
μr – relative permeability of the material.
A – cross-section area of the conductor.
• Its SI unit is AT / Wb (ampere-turns / Weber).
21
https://circuitglobe.com/what-is-magnetic-reluctance.html
Fig.6 Magnetic circuit
22. Terms Used in Magnetic Circuit
• Magnetic Permeance: It is the measure of the ease with which flux
can be set up in a material.
• Analogous to the conductance in an electrical circuit.
• Reciprocal of the reluctance (S) of the material in a magnetic circuit. It
is denoted by P.
• Measured in Weber per ampere turns (Wb/AT) or Henry (H).
22
https://circuitglobe.com/what-is-
permeance.html#:~:text=Definition%3A%20It%20is%20the%20measure,conductance%2
0in%20an%20electrical%20circuit.
23. Terms Used in Magnetic Circuit
• Magnetic Permeability: The magnetic permeability is defined as the
property of the material to allow the magnetic line of force to pass
through it.
• It supports the development of the magnetic field.
• SI unit is Henry per meter (H/M or Hm2) or newton per ampere
square (N-A2).
• It is directly proportional to the number of lines passing through it.
• The permeability of the air or vacuum is represented by μ0 which is
equal to 4π×10-7 H/m.
23
24. Terms Used in Magnetic Circuit
• It is equal to the ratio of the field intensity to the flux density of the
material. It is expressed by the formula shown below.
• Where, B – magnetic flux density
H – magnetic field intensity
• Relative permeability: The relative permeability of the material is the
comparison of the permeability concerning the air or vacuum.
24
https://circuitglobe.com/magnetic-permeability.html
25. Applications of Magnetic Circuit
These are used in motors and generators.
These are used in speakers.
These are used in transformers.
Magnetic strip are used in bank ATM cards, library cards etc.
These are preferred for tape recorders.
These are used in magnetic resonance imaging (MRI)
machines.
25
26. Faraday’s Laws of Electromagnetic Induction
• In 1831, Micheal Faraday formulated two laws on the basis of
experiments. These laws are called Faraday’s Laws of electromagnetic
induction.
26
https://www.electrical4u.com/faraday-law-of-electromagnetic-induction/
Fig.1 Faraday’s Law
27. Laws of Electromagnetic Induction
• First Law: It states that whenever a current carrying conductor is
placed in a varying magnetic field an emf is induced, if the conductor
circuit is closed current will be induced which is called induced
current.
27
https://www.daenotes.com/electronics/basic-electronics/faraday-laws-of-electromagnetic-induction
Fig.2 Faraday’s First Law
28. Laws of Electromagnetic Induction
• Second law: Second law states that an
induced emf is equal to the rate of
change of flux linkages.
• Flux linkage is equal to the product of
turns N of coil and flux associated with
it.
28
https://aninagmafae05.wordpress.com/2019/01/25/2-
concepts-brought-together-and-functions-as-one-
%F0%9F%92%9E/
Fig.3 Faraday’s Second Law
29. Derivation of Electromagnetic Induction
• Consider a magnet is approaching towards a coil, number of turns are
N in a coil and flux are Φ1 and Φ2.
Initial flux linkage = N Φ1
Final flux linkage = N Φ2
Changes in flux linkages = N Φ2 - N Φ1 = N(Φ2 - Φ1)
If N(Φ2 - Φ1) = Φ
Then changes in flux linkage = N Φ
Rate of change of flux linkage = N Φ/t weber/sec.
Now taking derivative of right hand side we get
Rate of change of flux linkage = NdΦ/dt
29
………………………………………(1)
………………………………………(2)
……………(3)
………………………………………(4)
………………………………………(5)
………………………(6)
………………………………………(7)
30. Derivation of Electromagnetic Induction
• But according to faraday’s law of electromagnetic induction, the rate
of change of flux linkage is equal to the induced emf so we will get:
E = -NdΦ/dt volt
• Here negative sign represents the direction of induced current in the
conductor will be such that magnetic field produced by it will oppose
due to which it produces.
30
31. How to increase EMF induced in a coil
• By increasing the number of turns in the coil.
• By increasing magnetic field strength B.
• By increasing the speed of the relative motion between the coil and
the magnet – the coil will cut the lines of flux at a faster rate, so more
induced emf would be produced.
31
32. Application of Faraday’s Law
The function of power transformer is based on faraday’s law.
The basic working principle of the electrical generator is Faraday’s
law of mutual induction.
The Induction cooker is the fastest way of cooking. It also works on
the principle of mutual induction.
Electromagnetic Flow Meter is used to measure the velocity of
certain fluids.
32
33. Summary
Introduction to magnetic circuit.
Different terms used in magnetic circuit.
Concept of mmf and magnetic flux.
Concept of magnetic permeance and magnetic permeability.
Types of magnetic circuit.
Applications of magnetic circuit.
33
34. Frequently Asked Questions
What is the difference between mmf and emf?
Define magnetic field intensity and reluctance.
What do you mean by magnetic permeance?
Classify the types of magnetic circuit.
Write down the applications of magnetic circuit.
34
35. Practice Questions
1. Ohm’s law for magnetic circuits is _________
a) F=ϕS
b) F=ϕ/S
c) F=ϕ2S
d) F=ϕ/S2
2. What happens to the MMF when the magnetic flux decreases?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
35
36. Practice Questions
3. What is MMF?
a) Magnetic Machine Force
b) Magnetomotive Force
c) Magnetic Motion Force
d) Magnetomotion Force
4. The equivalent of the current I in magnetic ohm’s law is?
a) Flux
b) Reluctance
c) MMF
d) Resistance
36
37. To make students understand
• Concepts of magnetic circuits
with its various terms
• Classification of magnetic circuit.
• Applications of magnetic circuit.
37
LEARNING
OUTCOMES
