by Nannapaneni Narayana Rao Edward C. Jordan Professor Emeritus

1. Fundamentals of Electromagneticsfor Teaching and Learning:A Two-Week Intensive Course for Faculty inElectrical-, Electronics-, Communication-, and Computer- Related Engineering Departments in Engineering Colleges in India by Nannapaneni Narayana Rao Edward C. Jordan Professor Emeritus of Electrical and Computer Engineering University of Illinois at Urbana-Champaign, USA Distinguished Amrita Professor of Engineering Amrita Vishwa Vidyapeetham, India

2. Program for Hyderabad Area and Andhra Pradesh FacultySponsored by IEEE Hyderabad Section, IETE Hyderabad Center, and Vasavi College of EngineeringIETE Conference Hall, Osmania University CampusHyderabad, Andhra PradeshJune 3 – June 11, 2009Workshop for Master Trainer Faculty Sponsored byIUCEE (Indo-US Coalition for Engineering Education)Infosys Campus, Mysore, KarnatakaJune 22 – July 3, 2009

3. Module 3 Maxwell’s Equations in Differential Form 3.1 Faraday’s law and Ampere’s Circuital Law 3.2 Gauss’ Laws and the Continuity Equation 3.3 Curl and Divergence

4. Instructional Objectives 16. Obtain the simplified forms of Faraday’s law and Ampere’s circuital law in differential forms for any special cases of electric and magnetic fields, respectively, or the particular differential equation that satisfies both laws for a special case of electric or magnetic field 17. Determine if a given time-varying electric/magnetic field satisfies Maxwell’s curl equations, and if so find the corresponding magnetic/electric field, and any required condition, if the field is incompletely specified 18. Find the magnetic field due to one-dimensional static current distribution using Maxwell’s curl equation for the magnetic field 19. Find the electric field due to one-dimensional static charge distribution using Maxwell’s divergence equation for the electric field

5. Instructional Objectives (Continued) 20. Establish the physical realizability of a static electric field by using Maxwell’s curl equation for the static case, and of a magnetic field by using the Maxwell’s divergence equation for the magnetic field 21. Investigate qualitatively the curl and divergence of a vector field by using the curl meter and divergence meter concepts, respectively 22. Apply Stokes’ and divergence theorems in carrying out vector calculus manipulations

6. 3.1 Faraday’s Law and Ampère’s Circuital Law (EEE, Sec. 3.1; FEME, Secs. 3.1, 3.2)

7. Maxwell’s Equations in Differential Form Why differential form? Because for integral forms to be useful, an a priori knowledge of the behavior of the field to be computed is necessary. The problem is similar to the following: There is no unique solution to this.

8. However, if, e.g., y(x) = Cx, then we can find y(x), since then On the other hand, suppose we have the following problem: Then y(x) = 2x + C Thus the solution is unique to within a constant. 3-7

9. 3-8 FARADAY’S LAW First consider the special case and apply the integral form to the rectangular path shown, in the limit that the rectangle shrinks to a point.

10. 3-9

11. General Case 3-10

12. 3-11 Lateral space derivatives of the components of E Time derivatives of the components of B

13. The terms on the left sides are the net right-lateral differentials of pairs of components of E. For example, in the first equation, it is the net right-lateral differential of Ey and Ez normal to the x-direction. The figure below illustrates (a) the case of zero value, and (b) the case of nonzero value, for this quantity. 3-12

14. Combining into a single differential equation, 3-13 Differential form of Faraday’s Law

15. AMPÈRE’S CIRCUITAL LAW Consider the general case first. Then noting that we obtain from analogy, 3-14

16. Thus Special case: 3-15 Differential form of Ampère’s circuital law

17. 3-16 E3.1 For in free space find the value(s) of k such that E satisfies both of Maxwell’s curl equations. Noting that

18. 3-17

19. Thus, 3-18 Then, noting that we have from

20. 3-19

21. 3-20

22. 3-21 Comparing with the original given E, we have Sinusoidal traveling waves in free space, propagating in the z directions with velocity,

23. E3.2.

25. Review Questions 3.1. Discuss the applicability of integral forms of Maxwell’s equations versus that of the differential forms for obtaining the solutions for the fields. 3.2. State Faraday’s law in differential form for the special case of E = Ex(z, t)ax and H = Hy(z, t)ay . How is it derived from Faraday’s law in integral form? 3.3. How would you derive Faraday’s law in differential form from its integral form for the general case of an arbitrary electric field? 3.4. What is meant by the net right-lateral differential of the x- and y- components of a vector normal to the z- direction? Give an example in which the net right-lateral differential of Ex and Ey normal to the z-direction is zero, although the individual derivatives are nonzero. 3.5. What is the determinant expansion for the curl of a vector in Cartesian coordinates?

26. Review Questions (Continued) 3.6. State Ampere’s circuital law in differential form for the general case of an arbitrary magnetic field. How is it obtained from its integral form? 3.7. State Ampere’s circuital law in differential form for the special case of H = Hy(z, t)ay . How is it derived from the Ampere’s circuital law for the general case in differential form? 3.8. If a pair of E and B at a point satisfies Faraday’s law in differential form, does it necessarily follow that it also satisfies Ampere’s circuital form and vice versa? 3.9. Discuss the determination of magnetic field for one dimensional current distributions, in the static case, using Ampere’s circuital law in differential form, without the displacement current density term.

27. Problem S3.1. Obtaining the differential equation for a special case that satisfies both of Maxwell’s curl equations

28. Problem S3.2. Finding possible condition for a specified field to satisfy both of Maxwell’s curl equations

29. Problem S3.3. Magnetic field due to a one-dimensional current distribution for the static case

30. Problem S3.3. Magnetic field due to a one-dimensional current distribution for the static case (Continued)

31. Problem S3.3. Magnetic field due to a one-dimensional current distribution for the static case (Continued)

32. 3.2 Gauss’ Laws and the Continuity Equation (EEE, Sec. 3.2; FEME, Secs. 3.4, 3.5, 3.6)

33. GAUSS’ LAW FOR THE ELECTRIC FIELD 3-32

35. The quantity on the left side is the net longitudinal differential of the components of D, that is, the algebraic sum of the derivatives of components of D along their respective directions. It can be written as which is known as the “divergence of D.” Thus, the equation becomes 3-34

36. 3-35 The figure below illustrates the case of (a) zero value, and (b) nonzero value for . E3.3 Given that Find D everywhere.

37. 3-36 Noting that r = r (x) and hence D = D(x), we set

38. Thus, which also means that D has only an x-component. Proceeding further, we have where C is the constant of integration. Evaluating the integral graphically, we have the following: 3-37

39. r r0 3-38 From symmetry considerations, the fields on the two sides of the charge distribution must be equal in magnitude and opposite in direction. Hence, C = – r0a

40. 3-39

41. r r GAUSS’ LAW FOR THE MAGNETIC FIELD From analogy Solenoidal property of magnetic field lines. Provides test for physical realizability of a given vector field as a magnetic field.

42. LAW OF CONSERVATION OF CHARGE r r 3-41 Continuity Equation

43. SUMMARY (4) is, however, not independent of (1), and (3) can be derived from (2) with the aid of (5). 3-42 (1) (2) (3) (4) (5)

44. The interdependence of fields and sources through Maxwell’s equations Ampere’s Circuital Law (2) Law of Conservation of Charge (5) Faraday’s Law (1)  Gauss’ Law for E (3)

45. Review Questions 3.10. State Gauss’ law for the electric field in differential form. How is it derived from its integral form? 3.11. What is meant by the net longitudinal differential of the components of a vector field? Give an example in which the net longitudinal differential of the components of a vector field is zero, although the individual derivatives are nonzero. 3.12. What is the expression for the divergence of a vector in Cartesian coordinates? 3.13. Discuss the determination of electric field for one dimensional charge distributions, in the static case, using Gauss’ law for the electric field in differential form.

46. Review Questions (Continued) 3.14. State Gauss’ law for the magnetic field in differential form. How is it obtained from its integral form? 3.15. How can you determine if a given vector field can be realized as a magnetic field? 3.16. State the continuity equation. 3.17. Summarize Maxwell’s equations in differential form and the continuity equation, stating which of the equations are independent. 3.18. Discuss the interdependence of fields and sources through Maxwell’s equations.

47. Problem S3.4. Finding the electric field due to a one-dimensional charge distribution for the static case

48. Problem S3.5. Finding the condition for the realizability of a specified vector field as a certain type of field

49. Problem S3.6. Determination of the group belonging to a specified vector field, based on its physical realizability

50. 3.3 Curl and Divergence(EEE, Sec. 3.3, App. B ; FEME, Secs. 3.3 and 3.6, App. B)