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? WHAT GOOD IS IT?

WHAT GOOD IS IT? Tongues in trees, books in the running brooks, Sermons in stones, and good in everything? -quoted by

When I was growing up, I spent most weekends with my two cousins, Steve and Stan. Their interests were fairly different from mine, and sometimes I just stayed in their room and read or worked on some project. One project in particular was the construction of a strobe light. This was before they were integral parts of cameras, discos or even of the psychedelic scene. I had read about them and how they could seem to stop fast action. I wanted to build one and use it at night to see how moths fly. Anyway, I recall sitting on the floor trying to wire the parts together from a diagram. I was frustrated and Stan asked me to tell to him once again what I was doing. After I tried to explain it, he just looked at me and asked, “What good is it?” I must have muttered something in reply, but it was not very memorable. I tried to build the strobe because I found it fascinating. Even today, although I am often asked to justify the practical purposes of my research, I do not think about it very much. That is not why I do research. Many of the modern miracles that we all take for granted began as observations, toys, or hobbies. They then were taken by and studied for the sake of knowledge with practical technologies flying from them along the way. No phenomena follow this description better than those of electricity and . Look around you. Observe how much your world is influenced by electricity and magnetism. A modern American home must have electricity just to operate. Its walls are filled with wires that provide to electrical outlets, lights, and air-conditioning systems. Porch lights, streetlights, and the occasional diabolical bug zapper will punctuate even a stroll down most streets. In the homes, we cook and prepare our meals, heat our water, and dry our hair by electricity. We entertain ourselves with electronic televisions, radios, and stereos. In fact, electricity has insinuated itself so completely into our lives, that we would have a very hard time living without it. When I was in Russia this past summer I visited a small village called Bykee. It had about 10 houses with a single, deeply rutted road that passed through it. All of the village houses got their water from a well, but they all had electricity.

ELECTRICITY & MAGNETISM I feel a Want of Terms here and doubt much whether I shall be able to make this intelligible. -Benjamin Franklin

The phenomenon of electricity, at least static electricity, had been known for millennia. In fact, is Greek for , one of the substances famous for producing a static charge when rubbed. Although known, static electricity was nothing more than a curiosity until the 18th Century. Benjamin Franklin (1706-1790, USA), was one of the first to explore electricity. He did so after he was given a static electricity generator by a friend in Britain. He became so immersed in the study of electricity in 1746 that almost everything else in his life took second place. He began a set of experiments that led him to write a series of papers that were well-received (after some initial jokes about a colonial yokel) at the Royal Society and elsewhere in Europe. In 1752, he conducted his most famous experiment with the kite, which helped to confirm that that and electricity were the same things. Based on that, he initiated experiments that led to the practical application of the lightning rod, an invention that saved and continues to save many buildings from destruction. Those and other experiments with electricity convinced Franklin that electricity moved from one place to another as a fluid. He was not sure which way the fluid went, but he guessed that the fluid moved from an object of excess to an object of deficiency. This was his explanation for why oppositely charged objects seemed to cancel each other out. He invented the terms positive and negative charge to differentiate between the two conditions. Although little was really known about the new, mysterious force of electricity, it did exert a force (or charge) that could either attract or repel another charged object. Charles Augustin de (1736-1806, France) examined the force between charged particles and discovered that electricity acted at a distance, and, like gravity, diminished according to the inverse square of the distance between the charges. That is, the charge of object 1 times the charge of object 2 divided by the distance between them squared can be expressed in units of force. This became known as Coulomb’s Law (see Figure 4-13).

1 Electricity works for us because we make it move in a circuit. In this sense, the movement of electricity is similar to the movement of water. In fact, the similarity does not stop there nor is it superficial. Electricity conducts through a metal wire like water moves through a pipe. If the pipe is smaller, less water gets through the pipe each second. Similarly, if a wire gets smaller, less electricity moves through it each second. Water moves downhill or as a consequence of water pressure in a pipe. moves as a consequence of electrical pressure from the power source. This is called the .

FIGURE 4-13. An illustration of Columb’s Law with balls of charge 1 and charge 2 repelling with a force to push them distance d apart.

Volt is named after Allesandro Volta (1745-1827), the man who invented the first chemical battery. His battery (or pile as he called it) was a layer cake of different metal disks with felt soaked in a weak acid between the metal disks. Volta tried to impress Napoleon with his idea, but he was unsuccessful at first. However, Volta did impress the scientific community with a reliable source of electrical power. This led to the use of electricity for many explorations in physics, chemistry, etc. Now, the battery is a necessary component of many things in the household, including the computer on which I am writing this. The power of a battery was its ability to make positive and negative charges at the poles of the battery; the greater the difference in charge, the greater the voltage. It was the voltage that provided the electrical pressure to move an electrical current in a wire. Andre-Marie Ampere (1775-1836 France) studied this movement of electrical charges in an electrical circuit. We now refer to the flow of electrical charge as amp (short for Ampere). Throughout the initial period of study, the Franklin theory of electrical fluid remained the prevailing view. While electricity had been known for only a short time, magnetism had been studied for millennia. Magnetite, a naturally occurring magnetic ore or lodestone is relatively common and, like any other , causes nails and other iron objects to jump. William Gilbert (1544-1603; England), physician to Queen Elizabeth I also studied and wrote about . He concluded that all magnets have two poles. Also, like magnetic poles repel each other while opposite magnetic poles attract. It wasn’t until Hans Christian Oersted (1770-1851, Denmark) was switching a current on and off during a lecture in Denmark in 1820 that he saw evidence of the relationship between electricity and magnetism. When current flowed through a wire that was suspended over a compass, the needle in the compass moved to a position perpendicular to the wire. Ampere interpreted Oersted’s observation of the interactions between electricity and magnetism in a Newtonian way. He described, mathematically, point forces acting at a distance from each other. In what is now called Ampere’s Law, which stated that a changing electrical charge or current produced a magnetic effect. In England, however, Oersted’s observation led to a revolutionary new way of viewing electrical and magnetic phenomena by a brilliant self-taught experimental genius.

2 Several important results may be deduced from the properties of lines of force. –

Michael Faraday (1791-1867, England) did not have proper schooling. In fact, he was self-educated. He worked in a bookbindery and read many of the books that came through his shop. One happened to be a portion of the third edition of the Encyclopedia Britannica. In particular, he read the 127-page article about electricity. At that point he became interested in science. By 1810 he began to attend lectures by the renowned chemist, Sir (1778-1829, England). About a year later, Davy became temporarily blinded by an explosion in his laboratory and hired Faraday to be his eyes and his hands. Soon, Faraday was performing his own experiments in Davy’s laboratory. He discovered benzene, made the first chlorinated and ethylene. He did pioneering work in the field of steel alloys and produced heavy optical glass. In 1821 Faraday heard of Oersted’s work and began to explore the strange connection between electricity and magnetism. He made a wire that circled a magnet when a current was passed through it. He also showed that a magnet would rotate around a wire carrying current. Because he did not have a background in mathematics, he did not understand Ampere’s explanation of electromagnetism. Instead, Faraday began to describe the phenomena in terms of physical models. He began to think of electricity and magnetism as fields or lines of force that extended from the wire or from the magnet. The lines of force interacted to create the electromagnetic phenomena that he had observed. Later, Faraday used a bar magnet and passed it through a coil of wire and noticed that the magnet induced a current in the wire (see Figure 4-14). However, when the magnet was stationary, the current stopped. He speculated that as the magnetic lines of force cut through the wire, they set into motion an electrical force. Likewise, he discovered that when a current flows in a wire, it creates a that circles that wire. Thus, Faraday, using his physical model to visualize the phenomenon, defined the Law of Induction or the electrical effect of changing a magnetic field. In addition, he used the concept of induction to create the first electric motor.

FIGURE 4-14. A diagram of Faraday's experiment. The magnetic field moving past the wire induced a current to move in the wire.

Carl Friedrich Gauss (1777-1855, Germany) was a mathematician whose interests ranged from pure mathematics to astronomy and physics. In 1832 Gauss used the concept of the field to generalize Coulomb’s Law into what is now called Gauss’ Law for Electricity. Later, he became very interested in magnetism and

3 magnetic fields. He attempted to measure magnetic field strengths over a large area in an attempt to map the Earth’s magnetic field. While doing so, he formulated a mathematical law intended to describe the magnetic field called Gauss’ Law for Magnetism. The most important outcome of which was that there are no magnetic monopoles. That is, no matter how small, a magnet always has both a north and south pole. James Clerk Maxwell (1831-1879, United Kingdom) had one of the most expansive minds of the 19th Century. His interests covered almost all aspects of physics, and his influence was remarkable for one with such a short life. Not only was he a careful experimentalist with an obsession for exact measurements, but he also was an influential writer because of his extraordinary ability to synthesize information. Thus, he influenced mechanics and thermodynamics. However, he was best known for his synthesis of electromagnetic theory. Like Faraday, Maxwell attempted to model physical phenomena. He viewed the ether as a field filled with hexagons of magnetic force each surrounded by small spheres of electrical force (Figure 4-15). As the electrical spheres moved, the wheels of magnetic force turned thus producing vortices of magnetism within the ether. Conversely, if the ether were subjected to a magnetic force, the turning wheels would push along the electrical spheres. He used this to explain the relationship between electricity and magnetism and to show how a single ether medium could accommodate both of them. Like Gauss, though, Maxwell generalized electromagnetic phenomena mathematically. In fact he distilled electromagnetism into four elegant differential equations that he published in 1873. The four equations were: Gauss’ Law for Electricity, Gauss’ Law for Magnetism, Ampere’s Law, and Faraday’s Law of Induction (Table 4-1). He put them all into the same form and several unexpected consequences emerged. The most important one was a calculation for the speed of electromagnetic wave propagation, which turned out to be about the experimentally derived speed of light. Because of that and other relationships between light, magnetism, and electricity, Maxwell theorized that visible light must also be an electromagnetic wave. This simplified things very much in that only a single ether would be required to transmit all of three of them. Other very far-reaching outcomes were the possibilities of electromagnetic waves with frequencies longer and shorter than those of visible light. This led to a search for what we now call the electromagnetic spectrum (Figure 4-16). The other more subtle, but ultimately more revolutionary outcome was the apparent constancy of the speed of light.

FIGURE 4-15. Maxwell’s model of the electromagnetic ether with turning wheels of magnetism surrounded by smaller spheres of electricity.

After the publication of his electromagnetic theory, Maxwell was appointed Cavendish Professor at Cambridge where he spent time designing and building the influential Cavendish Laboratory. In addition, he spent five years editing and compiling the unpublished electrical papers of Henry Cavendish (1731-1810, England). By the time he was finished, Maxwell was overcome with a debilitating illness that finally killed

4 him in 1879. Maxwell never saw the outcomes of his electromagnetic theory either from the perspectives of pure or applied science. Nevertheless, his theory ultimately led to inventions like the radio and radar. It also provided with the impetus to formulate the Special Theory of Relativity and to Albert Michelson (1852-1931, USA) to seek to detect the movement of the earth through the ether.

SCIENCE, PURE AND APPLIED Why, sir, there is every possibility that you will soon be able to tax it.1 -attributed to Michael Faraday

The exchange between Gladstone and Faraday likely is apocryphal because there are no contemporary accounts of such a conversation. However, it does illustrate the tension between the nonscientist’s wish for a better or more comfortable world and the scientist’s desire to understand. The motives of pure science, admittedly, are selfish. However, in the end, a society is better off knowing more about electromagnetism than the invention of a whole pile of new electrical gadgets. Thomas Alva Edison (1847-1931, USA), the Wizard of Menlo Park, amazed the world with a whole string of inventions whose impacts certainly changed the ways that we live. Still, when he wanted to improve and generalize the light bulb, his most notable invention, Edison called on a mathematician to model it according to electromagnetic formulas. Even though Edison held more than 1,000 patents, Norbert Wiener claimed that Edison’s most enduring “invention” was the discovery that in a hot light bulb even a vacuum conducts electricity, a phenomenon now known as the Edison Effect, his only real scientific discovery

TABLE 4-1 Maxwell’s Equations of Electromagnetism modified from Halliday and Resnick (1970). Gauss’ Law for Electricity describes the . Gauss’ Law for Magnetism describes the magnetic field. Ampere’s Law describes the magnetic effect of a changing electric field or current. Faraday’s Law of Induction describes the electric effect of a changing magnetic field.

FIGURE 4-16. The Electromagnetic Spectrum. The ranges for the different kinds of waves are approximate and given in logarithmic scale in meters. Overlaps indicate how the waves are used or treated, because electromagnetic phenomena come in a continuum of wavelengths. The background shading indicates the relative energy of the waves.

Applied Science generally provides temporary solutions to permanent problems. The light bulbs of today are not the same as those of Edison’s day, nor will the lamps of the future necessarily be familiar to you who read this today. What I am certain of, though, is that the laws of electromagnetism will govern the lamps of the future. So, what good was immediately realized by the work of Franklin, Coulomb, Ampere,

1 The supposed response by Michael Faraday to Prime Minister William Gladstone’s question, “What good is an electric motor?”

5 Oersted, Faraday, Gauss, and Maxwell? It is difficult for us in our electrical world to look back at a time when electricity was a source of scientific curiosity. Some, like Benjamin Franklin put his observations to use in the form of lightning rods. However, most were curious and were just attempting to answer the riddles of nature. I intended this story about electricity to illustrate the importance of primary research to a society. Many times, primary research leads down blind alleys and into dark rooms. But, sometimes research can lead to a well-lit room and a brighter future for us all. - 1996, revised 2004 References: Billington, David P. 1996. The Innovators, The Engineering Pioneers Who Made America Modern. John Wiley and Sons, Inc. New York Boorstin, Daniel J. 1983. The Discoverers, A History of Man’s Search to Know his World and Himself. Vintage Books, A Division of Random House, New York. Burke, James. 1985. The Day the Universe Changed. Little, Brown and Company. Boston Einstein, Albert and Leopold Infeld. 1938. The Evolution of Physics, The Growth of Ideas From Early Concepts to Relativity and Quanta. Simon and Schuster. New York. Faraday, Michael. (1910, reprinted 1993). The Forces of Matter. Promethius Books. Buffalo, NY. Fay, Bernard. 1929. Franklin. Little, Brown, & Co. Boston. Gribben, John. 2002. The Scientists. Random House. New York. Halliday, David and Robert Resnick. 1970. Fundamentals of Physics. John Wiley and Sons, Inc. New York Harre, Rom. 1981. Great Scientific Experiments, 20 Experiments that Changed Our View of the World. Phaidon Press, Ltd. Oxford. Mason, Stephen F. 1962. A History of the , Collier Books. New York. Mahon, Basil. 2003. The Man Who Changed Everything, The Life of James Clerk Maxwell. John Wiley & Sons. Hoboken, NJ. Maxwell, James C. 1873 (reprinted 2002). A Treatise on Electricity and Magnetism. Oxford University Press. Oxford, UK. Wiener, Norbert. 1993. Invention. The MIT Press. Cambridge, Mass.

6 Questions to Think About

1. What are some distinctions between the pure and applied sciences?

2. Beyond flying a kite, what did Benjamin Franklin contribute to science?

3. Coulomb defined the electrical force mathematically and showed that it was like gravity in what ways?

4. Why was the battery so important in the new study of electricity?

5. What phenomenon did Oersted observe? How did his observation cause Faraday to change physics?

6. How is the magnetic force different from the electrical force?

7. What is the importance of Maxwell’s equations? What two unexpected predictions came from them?

8. Would you consider Edison to be a scientist?

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