This document provides an introduction to electromagnetic fields. It discusses the electromagnetic model and different approaches to developing scientific theories, including the inductive and deductive approaches. Key topics covered include: - The differences between circuit theory and field theory in electromagnetic analysis. - An overview of the basic quantities in electromagnetic models, including electric charges, electric field intensity, magnetic flux density, and others. - Definitions of source quantities like electric charge, current density, and field quantities like the electric and magnetic fields. - Explanations of important field quantities like the electric field intensity vector E and magnetic field intensity vector H.

1. ELECTROMAGNETIC FIELDS
Dr.K.G.SHANTHI
Professor/ECE
shanthiece@rmkcet.ac.in
Circuit theory Vs Field theory
Inductive Approach Vs Deductive approach
Electromagnetic model

2. UNIT-I: INTRODUCTION
✘ Electromagnetic model
✘ Units and constants
✘ Review of vector algebra
✘ Rectangular, cylindrical and spherical coordinate systems
✘ Line, surface and volume integrals
✘ Gradient of a scalar field
✘ Divergence of a vector field
✘ Divergence theorem
✘ Curl of a vector field
✘ Stoke's theorem
✘ Null identities
✘ Helmholtz's theorem
2

3. ✘ Electromagnetics is a branch of physics or electrical engineering that
deals electric and magnetic phenomena.
✘ Electromagnetics is the study of the effects of electric charges at rest
and in motion.
✘ Both positive and negative charges are sources of an electric field.
✘ Moving Charges produce a current, which gives rise to a magnetic field.
✘ A Field is a spatial distribution of a quantity, which may or may not be a
function of time. A time-varying electric field is accompanied by a
magnetic field, and vice versa resulting in electromagnetic field.
✘ Electromagnetic theory is indispensable in the understanding of the
principle of cathode-ray oscilloscope, radar, satellite communication,
television reception, radio astronomy, microwave devices, Optical fiber
communication, instrument landing systems, electromechanical energy
conversion, antennas , electric machines, and remote sensing.
3

4. CIRCUIT THEORY Vs FIELD THEORY 4
S.No Circuit theory Field theory
1. It is a two dimensional analysis It is a three dimensional analysis
2. Deals with voltage (V) and current (I) Deals with Electric (E) and Magnetic (H) fields.
3. V and I are scalars E and H are vectors
4. V and I are functions of time (t) E and H are functions time (t) and space
variables (x, y, z) or (ρ, ϕ, z) or (r, θ, ϕ).
5. Radiation effects are neglected Radiation effects are considered.
6. Lumped components are involved Distributed components are involved.
7. Parameters of the medium are not
involved
Parameters of the medium (Permittivity μ and
Permeability ε are involved
8. Using circuit theory, transmitter and
receiver circuits can be analyzed and
designed. But it cannot be used to
design or analyze a medium like free
space
Using field theory, the medium also can be
designed and analyzed

5. 5
S.No Circuit theory Field theory
9. Circuit theory cannot be used to
analyze or design a complete
communication system
Field theory can be used where circuit
theory fails to hold good for the analysis
and design of a communication system.
10. Is useful at low frequencies Is useful at all frequencies, particularly at
high frequencies
11. Cannot be applied in free space Is applicable in free space.
12. Is simple Is complex but it is simplified by using
appropriate mathematics.
13. Basic laws are Ohms law, Kirchoff’s
laws
Basic laws are Coulomb’s law, Gauss’s law,
Ampere’s circuit law.
14. Basic theorems are Thevenin’s,
Nortan’s, Reciprocity, Superposition,
Maximum power transfer theorems
Basic theorems are Reciprocity, Helmholtz,
Stoke’s, Divergence and Poynting
theorems.
15. Basic equations are Mesh/Loop
equations.
Basic equations are Maxwell, Poisson,
Laplace and Wave.
16. Simple to understand Needs Visualization ability.

6. THE ELECTROMAGNETIC MODEL
6
Two approaches
in the
development of a
scientific subject
The Inductive
Approach
The Deductive
Approach

7. The Inductive Approach : Aims At Developing A Theory 7
1
• Observation
• A low-cost airline flight is delayed
2
• Observe a pattern
• Another 20 flights from low-cost airlines are delayed
3
• Develop a theory
• Low cost airlines always have delays
Limitations of an inductive approach:
A conclusion drawn on the basis of an inductive method can never be proven, but it can
be invalidated.
Example
You observe 1000 flights from low-cost airlines. All of them experience a delay, which is in
line with your theory. However, you can never prove that flight 1001 will also be delayed.
https://www.youtube.com/watch?v=yAjkQ1YqLEE

8. 8

9. The Deductive Approach: Aims at testing an
existing theory
9
1.
• Start with an existing theory
• All biological life depends on water to exist
2.
• Formulate a hypothesis based on existing theory
• All land mammals depend on water to exist
3.
• Collect data to test the hypothesis
• Study all land mammal species to see if they depend on water
4.
• Analyze the results: does the data reject or support the hypothesis?
• All land mammal species depend on water = support hypothesis

10. 10

11. 11
First, some basic quantities germane to the subject of study are defined
Eg: Voltages (V), currents (I), resistances (R), inductances (L), and capacitances (C)
Second, the rules of operation (the mathematics) of these quantities are
specified.
Eg: Algebra, ordinary differential equations
Third, some fundamental relations are postulated. These postulates or-laws are
invariably based on numerous experimental observations acquired under
controlled conditions and synthesized by brilliant minds.
Eg: Kirchhoff’s voltage and current laws
• The deductive approach is used in Electromagnetics .
• Three essential steps are involved in building a theory on
an idealized model:

12. 12
First, some basic quantities germane to the subject of study are defined
Eg: Electric Charges(q),electric Field Intensity E, Electric Flux Density D, Magnetic
Flux Density B, And Magnetic Field Intensity H.
Second, the rules of operation (the mathematics) of these quantities are
specified.
Eg: vector algebra; vector calculus, and partial differential equations.
Third, some fundamental relations are postulated. These postulates or-laws are
invariably based on numerous experimental observations acquired under
controlled conditions and synthesized by brilliant minds.
Eg: Coloumbs law, Gauss law, Maxwell equations
THE ELECTROMAGNETIC MODEL

13. Quantities in electromagnetic model
13
Quantities
Source
Quantities
Electric
charges at rest
or in motion
Field
Quantities
Electric field intensity E,
Electric flux density (or
electric displacement)D
Magnetic flux
density B, and
Magnetic field
intensity H.

14. 14
Electric charge (q or Q ) is fundamental property of matter and it exists only in positive or
negative integral multiples of charge of an electron.
Conservation of electric charge:
• It can neither be created nor be destroyed.
• Electric charges can move from one place to another and can be redistributed under the
influence of an electromagnetic field; but the algebraic sum of the positive and negative
charges in a closed (isolated) system remains unchanged
• The principle of conservation of electric charge must be satisfied at all times und under any
circumstances.
• It is represented mathematically by the equation of continuity.

15. Source Quantities
15
Source
Quantities
Electric charge
(q or Q )
Volume charge
density
Surface charge
density
Line charge density
Current:
Rate of change
of charge with
respect to time
Current density J:
Current per unit
area (A/m2)

16. 16
Field Quantities
• Electric field intensity E is the only vector needed in discussing electrostatics (effects
of stationary electric charges) in frees pace.
• Electric displacement vector D is useful in the study of electric field in material media.
• Magnetic flux density B is the only vector needed in discussing magnetostatics
(effects of steady electric currents) in free space, and is related to the magnetic force
acting on a charge moving with a given velocity.
• Magnetic field intensity vector H is useful in the study of magnetic field in material
media.

17. 17
Field Quantities: Electric field intensity E

18. 18
Field Quantities: Magnetic field intensity

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THANK YOU