Updated:  9/14/04
                  
           Chapter 21 Electromagnetic Induction and
                            Faraday's Law; AC Circuits

          A. Instruction to students:
                   Homework:
                        1) Read carefully all sections except 21-6, -8, and -15.
                            Sections 21-5 (Electric generators), -9 (Inductance),
                            -10 (Energy stored in a magnetic field), and -11 (LR circuit) are
                            for conceptual understanding only. 
                        2) Do all Examples in the text except 21-6, -7, -8, -11,and  -12.
                        3) Do all sample multiple choice problems posted.
                  Following formula and constants from Chapters 21 will be given
                  during the exams. Practice how to use and apply them.  
                                         \Phi = BA
                                         emf  =  - N (\Delta \Phi) / (\Delta t)
                                         Vp Ip = Vs Is
                                         emf = - M (\Delta I) / (\Delta t)   
                                         U = L I^2 / 2
                                         V = I X_L
                                         V = I X_C
                                         V = I Z
                                         Z = sqrt[ R^2 + (X_L - X_C)^2 ]
                                         X_L = 2 \pi f L
                                         X_C = 1 / ( 2 \pi f C)  
 
                                      
          B. Biomedical (and technological) application
                     Pacemaker in p639 following Eq. 21-8b.  (See also Section 19-8.)
                     Electric generators, Section 21-5, transformers, Section 21-7, and
                          electric resonances used in radio and TV, Section 21-14.


          C. Lectures and study guideline
 
                The main objective of this section is AC circuits of Section 21- 13 and physics leading to
                them:
                              Faraday's law and Lenz's law of Section 21-2, and
                              " a changing magnetic flux produces an electric field " of Section 21-4.
                The very basic concept in these is " induction " such as those in
                              " induced emf, "  and " induced current. "

                If you can understand how electric generators work (in Section 21-5) and how transformers
                work (in Section 21-7), you understand the concept of induction.  You should then proceed
                to the main objective, AC circuits.

                Familiarize yourself with the terms, their notations, and their units:
                                                    Electromotive Force    Emf    (V)      in p562
                                                    Magnetic flux   \Phi  (Wb, Weber)   1 Wb
                                                         Note: 1 Wb = 1 T m^2 = 1 N m / A = 1 J / A
                                                                            = 1 V s       
                                                                   (Remember 1 T = 1 N / A m,  from Chapter 20
                                                                                      1 J =  1 N m,  from 100A
                                                                                            =  1 V A s, from "power" in Chapter 18)
                                                    Resistance     R     (Ohm)                      
                                                    Capacitance  C      (F)                      1 F = 1 Coulomb / V
                                                    Inductance    L       (H, Henry)          1 H = 1 V s / A = 1 Ohm s
                                                    Inductive reactance, or impedance    X_L  (Ohm)
                                                    Capacitive reactance, or impedance  X_C (Ohm)                                                    
                                                    (Total) Impedance                            Z      (Ohm)

                Electromagnetism described in the six chapters, Chapters 16 - 21, is actually one subject.  
                As such, if you could not understand earlier chapters in these chapters, you would not be able
                to understand Section 21.  If this should be the case, do not hesitate to go back to the earlier
                chapters and to try to understand the materials in them.

                The next chapter, Chapter 22, will be an application of Chapter 21 (thus of all six chapters,
                conceptually)
                 
                In the second exam, all formula that were given in the first exam, together with the new formua
                will be given.