10 Introduction to Electric Potential and Electric Energy

In Electric Charge and Electric Field, we only began exploring electrical phenomena. Two of the most familiar and most useful aspects of electricity—especially in health and bioscience contexts—are electrical energy and voltage.

We know that electrical energy can be stored in batteries, transmitted long distances through power lines, and released suddenly in events such as lightning. In living systems, electrical effects also matter: ions move across cell membranes, creating voltage differences that help transmit information in nerves and trigger muscle contraction (including the coordinated contraction of cardiac muscle). Technologies such as ECGs, neural recording devices, and defibrillators all rely on controlling electric potential energy and voltage.

We also have everyday experience with voltages: batteries are typically a few volts, household outlets in the United States provide about 120 V, and transmission lines can reach hundreds of thousands of volts. But energy and voltage are not the same thing. A motorcycle battery, for example, is smaller than a car battery and stores less energy, yet both can provide the same voltage. Voltage tells you how much electric potential energy is available per unit charge, not the total amount of energy stored.

In this chapter, we will examine the relationship between voltage and electrical energy and begin exploring applications of electricity—ranging from engineered systems like circuits and power delivery to biomedical examples where voltage and energy transfer are essential for understanding physiology and medical devices.