10 Introduction to Electric Potential and Electric Energy

Figure 10.1 shows an automated external defibrillator (AED), a device that stores electrical energy and delivers a controlled electrical pulse to the heart. AEDs provide a real-world example of electric potential energy and voltage in medicine.

In the previous chapters, we introduced electric charge, electric forces, and electric fields. These concepts explain how charges interact. In this chapter, we introduce two equally important ideas: electric potential energy and electric potential, more commonly called voltage. These quantities describe the energy associated with electric charges and provide a convenient way to analyze many electrical systems.

Electrical energy is all around us. Batteries store it chemically, power plants generate it, and electrical grids deliver it over long distances to homes, hospitals, and industries. In living organisms, electrical energy is equally important. The movement of ions across cell membranes creates voltage differences that allow nerve cells to transmit signals, muscles to contract, and the heart to maintain its coordinated rhythm. Medical technologies such as electrocardiograms (ECGs), neural recording systems, pacemakers, and defibrillators all rely on controlling electrical energy and voltage.

Although the terms energy and voltage are often used together, they describe different physical quantities. Voltage measures the electric potential energy available per unit charge, whereas electrical energy depends on both the voltage and the amount of charge involved. For example, a motorcycle battery and a car battery both provide approximately 12 V, yet the larger car battery stores much more energy because it can supply far more charge.

Throughout this chapter, we will develop the relationship between electric potential energy and voltage and learn how these concepts simplify the analysis of electric fields. We will also explore examples from medicine and biology, where voltage differences across cell membranes and controlled energy transfer are fundamental to both normal physiology and modern diagnostic and therapeutic devices.