TAILIEUCHUNG - Electric Circuits, 9th Edition P6

Electric Circuits, 9th Edition P6. 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. | 26 Circuit Elements a b Figure The circuit symbols for a an ideal independent voltage source and b an ideal independent current source. Voltage and Current Sources Before discussing ideal voltage and current sources we need to consider the general nature of electrical sources. An electrical source is a device that is capable of converting nonelectric energy to electric energy and vice versa. A discharging battery converts chemical energy to electric energy whereas a battery being charged converts electric energy to chemical energy. A dynamo is a machine that converts mechanical energy to electric energy and vice versa. If operating in the mechanical-to-elec-tric mode it is called a generator. If transforming from electric to mechanical energy it is referred to as a motor. The important thing to remember about these sources is that they can either deliver or absorb electric power generally maintaining either voltage or current. This behavior is of particular interest for circuit analysis and led to the creation of the ideal voltage source and the ideal current source as basic circuit elements. The challenge is to model practical sources in terms of the ideal basic circuit elements. An ideal voltage source is a circuit element that maintains a prescribed voltage across its terminals regardless of the current flowing in those terminals. Similarly an ideal current source is a circuit element that maintains a prescribed current through its terminals regardless of the voltage across those terminals. These circuit elements do not exist as practical devices they are idealized models of actual voltage and current sources. Using an ideal model for current and voltage sources places an important restriction on how we may describe them mathematically. Because an ideal voltage source provides a steady voltage even if the current in the element changes it is impossible to specify the current in an ideal voltage source as a function of its voltage. Likewise if the only .

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