RI Chap 18 Electromagnetic Induction Lecture Notes

18 ELECTROMAGNETIC INDUCTION H2 Physics 9478 Content Page Introduction 2 18.1 Faraday’s Law of Electromagnetic Induction 2 18.2 Magnetic Flux and Magnetic Flux Linkage 3 18.3 Direction of Induced e.m.f. (or Current) 6 18.4 Metal Rod Moving Across a Uniform Magnetic Field 9 18.5 Rotating Disc in a Uniform Magnetic Field 13 18.6 Rotating Coil in a Uniform Magnetic Field (AC Generator) 15 18.7 Practical Applications of Electromagnetic Induction 17 18.8 Transformers 20 Summary 27 Appendix A 28 Appendix B 29 Appendix C 30 Learning Outcomes Candidates should be able to: (a) define magnetic flux as the product of the magnetic flux density and the cross -sectional area perpendicular to the direction of the magnetic flux density. (b) show an understanding of and use the concept of magnetic flux linkage. (c) recall and use φ = BA and N NBAφ = to solve problems, where N is the number of turns. (d) infer from appropriate experiments on electromagnetic induction: (i) that a changing magnetic flux can induce an e.m.f. ; (ii) that the direction of the induced e.m.f. opposes the change producing it ; (iii) the factors affecting the magnitude of the induced e.m.f. (e) recall and solve problems using Faraday's law of electromagnetic induction and Lenz's law. (f) explain simple applications of electromagnetic induction. (g) show an understanding of the principle of operation of a simple iron- core transformer and recall and solve problems using I I= =ss P pps NV NV for an ideal transformer.

Page | 2 Introduction We began our study on the relationship between electricity and magnetism in the previous chapter where we learned that an electric current (or moving charges) produces a magnetic field. As a result, when a current-carrying conductor or a moving charge is w ithin a magnetic field, it will experience a force. In this chapter, we will see that the converse happens. Experiments conducted by Michael Faraday in England in 1831 and independently by Joseph Henry in the United States the same year demonstrated that an e.m.f. could be induced by a changing magnetic field. This effect is known as electromagnetic induction. This discovery greatly revolutionized the production of electricity and has a significant impact on our daily lives. How electromagnetic induction was discovered 18.1 Faraday’s Law of Electromagnetic Induction  Observing Electromagnetic Induction Electromagnetic induction can be demonstrated easily using the laboratory apparatus shown in Fig. 18.1. A bar magnet is moved towards or away from a coil of wire which is connected to a sensitive galvanometer. It is found that: • no current is generated when the magnet is kept stationary relative to the coil (Fig. 18.1(a)), • a current is induced in the coil when the magnet is moved towards (Fig. 18.1( b)) or moved away (Fig. 18.1( c)) from the coi l, a