1. EMT 238/3 Electromagnetic Theory
Shamsul Amir bin Abdul Rais
12 September 2011

2. Basic Info This is course is implemented 100% through lecture.
The assessment will be as follows:
- 70% final exam
- 10% mid-term exam, scheduled on /11/2011
-20% assignment (lab test, PBL)
You will be broken into several groups for PBL

3. Basic Preparation
To go through this lecture, you would be needing basic math skills such as calculus, vector, coordinate systems, SI units, dimensions and linear and algebra(matrix, dot & cross product)
The main reference for this subject is “Electromagnetics with Application” Kraus/Fleisch, McGraw-Hill
All lecture notes, teaching plan and other things will be available at portal.

4. Examples of EM Applications

5. Dimensions and Units

9. Fundamental Forces of Nature

10. Charge: Electrical property of particles
Units: coulomb
One coulomb: amount of charge accumulated in one second by a current of one ampere.
1 coulomb represents the charge on ~ x 1018 electrons
The coulomb is named for a French physicist, Charles-Augustin de Coulomb ( ), who was the first to measure accurately the forces exerted between electric charges.
Charge of an electron
e = x C
Charge conservation
Cannot create or destroy charge, only transfer

11. Electrical Force
Force exerted on charge 2 by charge 1

12. Electric Field In Free Space
Permittivity of free space

13. Coulomb’s Law Electric field at point P due to single charge
Electric force on a test charge placed at P
Electric flux density D

14. Electric Field Due to 2 Charges

15. Electric Field due to Multiple Charges

16. Maxwell’s Equations
God said:
And there was light!

17. Current Density For a surface with any orientation:
J is called the current density

18. Convection vs. Conduction

19. Electric Field Due to Charge Distributions

22. Gauss’s Law
Application of the divergence theorem gives:

23. Applying Gauss’s Law
Construct an imaginary Gaussian cylinder of radius r and height h:

24. Electric Scalar Potential
Minimum force needed to move charge against E field:

25. Electric Scalar Potential

26. Electric Potential Due to Charges
For a point charge, V at range R is:
In electric circuits, we usually select a convenient node that we call ground and assign it zero reference voltage. In free space and material media, we choose infinity as reference with V = 0. Hence, at a point P
For continuous charge distributions:

27. Relating E to V

28. Cont.

29. (cont.)

30. Poisson’s & Laplace’s Equations
In the absence of charges:

32. Conduction Current Conduction current density:
Note how wide the range is, over 24 orders of magnitude

33. Conductivity ve = volume charge density of electrons
he = volume charge density of holes
e = electron mobility
h = hole mobility
Ne = number of electrons per unit volume
Nh = number of holes per unit volume

35. Resistance
Longitudinal Resistor
For any conductor:

36. G’=0 if the insulating material is air or a perfect dielectric with zero conductivity.

37. Joule’s Law
The power dissipated in a volume containing electric field E and current density J is:
For a coaxial cable:
For a resistor, Joule’s law reduces to:

38. Polarization Field
P = electric flux density induced by E

39. Electric Breakdown
Electric Breakdown

40. Boundary Conditions

41. Summary of Boundary Conditions
Remember E = 0 in a good conductor

43. Conductors
Net electric field inside a conductor is zero

44. Field Lines at Conductor Boundary
At conductor boundary, E field direction is always perpendicular to conductor surface

45. Capacitance

46. Capacitance
For any two-conductor configuration:
For any resistor:

48. Application of Gauss’s law gives:
Q is total charge on inside of outer cylinder, and –Q is on outside surface of inner cylinder

49. Electrostatic Potential Energy
Electrostatic potential energy density (Joules/volume)
Energy stored in a capacitor
Total electrostatic energy stored in a volume

50. Image Method
Image method simplifies calculation for E and V due to charges near conducting planes.
For each charge Q, add an image charge –Q
Remove conducting plane
Calculate field due to all charges