tailieunhanh - Fundamentals of Engineering Electromagnetics - Chapter 4

Năm 1831, Michael Faraday thực hiện thí nghiệm để kiểm tra xem hiện tại là sản xuất trong một vòng dây khép kín được đặt gần một nam châm, tương tự với dòng dc sản xuất từ trường. Thí nghiệm của ông cho thấy rằng điều này có thể được thực hiện, nhưng Faraday nhận ra rằng một dòng điện biến thiên theo thời gian trong vòng lặp này được thu thập trong khi nam châm đã được di chuyển về phía nó hay từ nó. Pháp luật ông đã xây dựng được gọi là định luật cảm ứng điện. | 4 Electromagnetic Induction Milica Popovic McGill University Montreal Quebec Branko D. Popovicy University of Belgrade Belgrade Yugoslavia Zoya Popovic University of Colorado Boulder Colorado To the loving memory of our father professor and coauthor. We hope that he would have agreed with the changes we have made after his last edits. Milica and Zoya Popovic . INTRODUCTION In 1831 Michael Faraday performed experiments to check whether current is produced in a closed wire loop placed near a magnet in analogy to dc currents producing magnetic fields. His experiment showed that this could not be done but Faraday realized that a time-varying current in the loop was obtained while the magnet was being moved toward it or away from it. The law he formulated is known as Faraday s law of electromagnetic induction. It is perhaps the most important law of electromagnetism. Without it there would be no electricity from rotating generators no telephone no radio and television no magnetic memories to mention but a few applications. The phenomenon of electromagnetic induction has a simple physical interpretation. Two charged particles charges at rest act on each other with a force given by Coulomb s law. Two charges moving with uniform velocities act on each other with an additional force the magnetic force. If a particle is accelerated there is another additional force that it exerts on other charged particles stationary or moving. As in the case of the magnetic force if only a pair of charges is considered this additional force is much smaller than Coulomb s force. However time-varying currents in conductors involve a vast number of accelerated charges and produce effects significant enough to be easily measurable. This additional force is of the same form as the electric force F QE . However other properties of the electric field vector E in this case are different from those of the yDeceased. 123 2006 by Taylor Francis Group LLC 124 Popovic et al. electric field vector of