# 1.1 Historical Timeline

The history of EM may be divided into two overlapping eras. The first is the classical era, during which the fundamental laws of electricity and magnetism were discovered and formulated. Building on these formulations, the modern era of the past 100 years ushered in the birth of the field of applied EM as we know it today.

# 1.1.1 EM in the Classical Era

Chronology 1-1 provides a timeline for the development of electromagnetic theory in the classical era. It highlights those discoveries and inventions that have impacted the historical development of EM in a very significant way, even though the selected discoveries represent only a small fraction of those responsible for our current understanding of electromagnetics. As we proceed through this book, some of the names highlighted in Chronology 1-1, such as those of Coulomb and Faraday, will appear again as we discuss the laws and formulations named after them.

The attractive force of magnetite was reported by the Greeks some 2800 years ago. It was also a Greek, Thales of Miletus, who first wrote about what we now call static electricity: He described how rubbing amber caused it to develop a force that could pick up light objects such as feathers. The term “electric” first appeared in print around 1600 in a treatise on the (electric) force generated by friction, authored by the physician to Queen Elizabeth I, William Gilbert.

About a century later, in 1733, Charles-François du Fay introduced the notion that electricity involves two types of “fluids,” one “positive” and the other “negative,” and that like-fluids repel and opposite-fluids attract. His notion of a fluid is what we today call electric charge. The invention of the capacitor in 1745, originally called the Leyden jar, made it possible to store significant amounts of electric charge in a single device. A few years later, in 1752, Benjamin Franklin demonstrated that lightning is a form of electricity. He transferred electric charge from a cloud to a Leyden jar via a silk kite flown in a thunderstorm. The collective eighteenth-century knowledge about electricity was integrated in 1785 by Charles-Augustin de Coulomb, in the form of a mathematical formulation characterizing the electrical force between two charges in terms of their strengths and polarities and the distance between them.

The year 1800 is noted for the development of the first electric battery by Alessandro Volta, and 1820 was a banner year for discoveries about how electric currents induce magnetism. This knowledge was put to good use by Joseph Henry, who developed one of the earliest electromagnets and dc (direct current) electric motors. Shortly thereafter, Michael Faraday built the first electric generator (the converse of the electric motor). Faraday, in essence, demonstrated that a changing magnetic field induces an electric field (and hence a voltage). The converse relation, namely that a changing electric field induces a magnetic field, was first proposed by James Clerk Maxwell in 1864 and then incorporated into his four (now) famous equations in 1873.

Maxwell’s theory, which predicted the existence of electromagnetic waves, was not fully accepted by the scientific community at that time. It was later verified experimentally by means of radio waves by Heinrich Hertz in the 1880s. X-rays, another member of the EM family, were discovered in 1895 by Wilhelm Röntgen. In the same decade, Nikola Tesla was the first to develop the ac motor, which was considered a major advance over its predecessor, the dc motor.

Despite the advances made in the 19th century in our understanding of electricity and magnetism and how to put them to practical use, it was not until 1897 that the fundamental carrier of electric charge, the electron, was identified and its properties quantified by Joseph Thomson. The ability to eject electrons from a material by shining electromagnetic energy, such as light, on it is known as the photoelectric effect.

# 1.1.2 EM in the Modern Era

Electromagnetics play a role in the design and operation of every conceivable electronic device, including the diode, transistor, integrated circuit, laser, display screen, bar-code reader, cell phone, and microwave oven, to name but a few. Given the breadth and diversity of these applications (Fig. 1-2), it is far more difficult to construct a meaningful timeline for the modern era than for the classical era. That said, one can develop timelines for specific technologies and link their milestone innovations to EM. Chronologies 1-2 and 1-3 present timelines for the development of telecommunications and computers, technologies that have become integral parts of today’s societal infrastructure. Some of the entries in these chronologies refer to specific inventions, such as the telegraph, the transistor, and the laser. The operational principles and capabilities of some of these technologies are highlighted in special sections called Technology Briefs that are scattered throughout this book.

# Figure 1-2 Electromagnetics is at the heart of numerous systems and applications.

NRAO/NASA

Jet Propulsion Laboratory/NASA

ABB

Fad82/Fotolia

John Slough/NASA

Ashley Tyler/US Air Force

Valentyn Volkov/123RF

Oleksiy Mark/Shutterstock

Source: Based on IEEE Spectrum

Figure 1 2 Full Alternative Text