Chapter 11: Practical Circuits

Every battery or power supply contains internal resistance due to its physical components, which causes the terminal potential difference to decrease below the electromotive force as current increases. The relationship between terminal potential difference, electromotive force, current, and internal resistance is expressed through fundamental equations that allow prediction of energy losses as heat within the power source. Students learn experimental methods to determine both the electromotive force and internal resistance of a cell by measuring voltage and current at various loads and analyzing the resulting linear relationship. The chapter then introduces potential dividers, which are circuits that produce a specific fraction of an input voltage using series resistors. This principle extends to sensor applications where light-dependent resistors and thermistors convert environmental changes into measurable voltage variations. Light-dependent resistors demonstrate linear resistance changes with light intensity, while negative temperature coefficient thermistors exhibit nonlinear resistance changes with temperature that require careful calibration. Finally, the potentiometer is presented as a precise measurement device that compares potential differences using a null method. By finding the balance point where a galvanometer shows zero deflection, the potentiometer eliminates errors from internal resistance and provides accurate measurements of electromotive force without drawing current from the cell being tested. The mathematical relationships and experimental techniques throughout the chapter enable students to analyze real circuits that contain resistance, measure unknown voltages accurately, and design sensor systems for practical applications.