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Electric Circuits, 9th Edition P21. Designed for use in a one or two-semester Introductory Circuit Analysis or Circuit Theory Course taught in Electrical or Computer Engineering Departments. Electric Circuits 9/e is the most widely used introductory circuits textbook of the past 25 years. As this book has evolved over the years to meet the changing learning styles of students, importantly, the underlying teaching approaches and philosophies remain unchanged. | 176 Inductance Capacitance and Mutual Inductance The inductor v - i equation b Figure 6.1 a The graphic symbol for an inductor with an inductance of L henrys. b Assigning reference voltage and current to the inductor following the passive sign convention. Section 6.3 describes techniques used to simplify circuits with series or parallel combinations of capacitors or inductors. Energy can be stored in both magnetic and electric fields. Hence you should not be too surprised to learn that inductors and capacitors are capable of storing energy. For example energy can be stored in an inductor and then released to fire a spark plug. Energy can be stored in a capacitor and then released to fire a flashbulb. In ideal inductors and capacitors only as much energy can be extracted as has been stored. Because inductors and capacitors cannot generate energy they are classified as passive elements. In Sections 6.4 and 6.5 we consider the situation in which two circuits are linked by a magnetic field and thus are said to be magnetically coupled. In this case the voltage induced in the second circuit can be related to the time-varying current in the first circuit by a parameter known as mutual inductance. The practical significance of magnetic coupling unfolds as we study the relationships between current voltage power and several new parameters specific to mutual inductance. We introduce these relationships here and then describe their utility in a device called a transformer in Chapters 9 and 10. 6.1 The Inductor Inductance is the circuit parameter used to describe an inductor. Inductance is symbolized by the letter L is measured in henrys H and is represented graphically as a coiled wire a reminder that inductance is a consequence of a conductor linking a magnetic field. Figure 6.1 a shows an inductor. Assigning the reference direction of the current in the direction of the voltage drop across the terminals of the inductor as shown in Fig. 6.1 b yields _ di V LdC 6-1 where v is