TABLE OF CONTENTS Resistors, capacitors, and inductors these are the three basic passive elements used in electrical circuits, either as individual devices or in combination. These elements are used as loads, delays, and current limiting devices. Capacitors are used as dc blocking devices, in level shifting, integrating, differentiating, filters, frequency determination, selection, and delay circuits. Inductive devices can be extended to cover analog meter movements, relays, audio to electrical conversion, electrical to audio conversion, and electromagnetic devices. They are also the basis for transformers and motors.
Passive components are extensively used in ac circuits for frequency selection, noise suppression, and so forth, and are always present as parasitic components, limiting signal response and introducing unwanted delays. These components also cause phase shift between voltages and currents, which has to be taken into account when evaluating the performance of ac circuits.
When a dc voltage is applied to the series resistor-capacitor circuit shown in Figure 3.1(a) a current flows in the elements, charging the capacitor. Figure 3.1(b) shows the input voltage step, the resulting current flowing, and the voltages across the resistor and the capacitor. Initially, all the voltage is dropped across the resistor. Although current is flowing into the capacitor, there is no voltage drop across the capacitor. As the capacitor charges, the voltage across the capacitor builds up exponentially, and the voltage across the resistor starts to decline, until eventually the capacitor is fully charged and current ceases to flow.
