26 Introduction to Circuits and DC Instruments

Electric circuits form the foundation of modern technology. They control how electrical energy is transferred, transformed, and used in devices ranging from flashlights and smartphones to medical instruments, communication systems, and supercomputers. Although electronic systems may contain millions or even billions of components, they are all governed by the same fundamental physical principles.

In the previous part, you learned how voltage drives electric current, how resistance limits current, and how these quantities are related through Ohm’s law. In this part, we extend those ideas to complete electrical circuits containing multiple components. By combining simple circuit elements in different ways, we can design systems that perform specific electrical functions, from controlling current flow to storing electrical energy.

This chapter begins by introducing the basic elements of direct-current (DC) circuits and the instruments used to measure electrical quantities such as voltage and current. We then investigate how capacitors behave when connected to DC voltage sources, showing how they store electrical energy and how circuits change over time as capacitors charge and discharge. The behavior of capacitors in alternating-current (AC) circuits will be explored in a later chapter.