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Agata Schweiss
Despite this long acquaintance with all sorts of electrical and magnetic phenomena, no one suspected until the early 1800s that the two were inextricably linked (let alone that these twin forces create waves of energy). Over the next century, however, a handful of brilliant thinkers and experimenters gradually unraveled the mysteries of electromagnetism.
Electromagnetism involves the interaction between electrically charged particles. It combines electricity and magnetism into a single theory and is responsible for various phenomena, such as the generation of electric currents and magnetic fields.
We use electromagnetism every day with electric motors, radio and television broadcasting, and medical equipment like MRI machines. To put it simply, it's how electric charges produce magnetic fields and how changing magnetic fields create electricity. Here are the groundbreaking contributions physicists made to the field of electromagnetism.
During a lecture in 1820, rsted, a Danish physicist, stumbled upon the first clue: He found that when he ran electricity through a wire, the needle of a compass held nearby would deflect from its normal alignment with magnetic north until it lay perpendicular to the current. In other words, he discovered that electric currents create magnetic fields.
Accounts differ as to whether rsted was looking for this result or accidentally discovered it. Regardless, it was the first sign of an intimate relationship between electricity and magnetism and a major inspiration for the next key player in the story.
In August 1831, he wound two coils of insulated wire around opposite sides of an iron ring. One was connected to a battery, thereby magnetizing the iron, and the other was connected to a galvanometer to detect electric current. Faraday wanted to see whether the magnetic field produced by the first wire would electrify the second.
At first, the results were puzzling. To his amazement, the galvanometer briefly registered a current in the second wire whenever he turned on the current in the first and again when he turned it off, but nothing in between. He realized it was not the mere presence of a magnetic field causing the current, but a change in the magnetic field. He later got the same outcome by moving a magnet in and out of a coil of wire.
Faraday had discovered a process known as electromagnetic induction and simultaneously invented the first electrical transformer. In fact, his work laid the foundation for much of the modern technology we hold most dear, including the infrastructure that generates and distributes power to our homes.
Due to his poor upbringing and lack of formal education, Faraday was always a far better experimenter than mathematician. But the same year he made his greatest discovery, the man who would give it a rigorous theoretical framework was born.
Maxwell correctly guessed that these waves were the stuff of visible light, and later researchers proved the same for the rest of the electromagnetic spectrum: gamma-rays, x-rays, ultraviolet, infrared, microwaves, and radio waves.
The paper (which later won him a Nobel prize) was an explanation of the photoelectric effect, in which light shining on a metal surface causes that surface to emit electrons. Physicists had been unable to explain this phenomenon with classical wave theory, so Einstein introduced a new concept: the quantization of light.
James Clerk Maxwell was one of the greatest scientists of the nineteenth century. He is best known for the formulation of the theory of electromagnetism and in making the connection between light and electromagnetic waves. He also made significant contributions in the areas of physics, mathematics, astronomy and engineering. He considered by many as the father of modern physics.
Maxwell was born in Edinburgh, Scotland in 1831. Even though most of his formal higher education took place in London, he was always drawn back to his family home in the hills of Scotland. As a young child, Maxwell was fascinated with geometry and mechanical models. When he was only 14 years old, he published his first scientific paper on the mathematics of oval curves and ellipses that he traced with pins and thread. Maxwell continued to publish papers on a variety of subjects. These included the mathematics of human perception of colors, the kinetic theory of gases, the dynamics of a spinning top, theories of soap bubbles, and many others.
Maxwell's early education took place at Edinburgh Academy and the University of Edinburgh. In 1850 he went on to study at the University of Cambridge and, upon graduation from Cambridge, Maxwell became a professor of natural philosophy at Marischal College in Aberdeen until 1860. He then moved to London to become a professor of natural philosophy and astronomy at King's College. In 1865, Maxwell's father died and he returned to the family home in Scotland to devote his time to research. In 1871 he accepted a position as the first professor of experimental physics at Cambridge where he set up the world famous Cavendish Laboratory in 1874.
While at Aberdeen, Maxwell was challenged by the subject of the Adams Prize of 1857: the motion of Saturn's rings. He had previously thought and theorized about the nature of the rings when he was only 16 years old. He decided to compete for the prize, and the next two years were taken up with developing a theory to explain the physical composition of the rings. He was finally able to demonstrate, by purely mathematical reasoning, that the stability of rings could only be achieved if they consisted of numerous small particles. His theory won him the prize and, more significantly, nearly a hundred years later, the Voyager 1 space probe proved his theory right.
Much of modern technology has been developed from the basic principles of electromagnetism formulated by Maxwell. The field of electronics, including the telephone, radio, television, and radar, stem from his discoveries and formulations. While Maxwell relied heavily on previous discoveries about electricity and magnetism, he also made a significant leap in unifying the theories of magnetism, electricity, and light. His revolutionary work lead to the development of quantum physics in the early 1900's and to Einstein's theory of relativity.
Maxwell began his work in electromagnetism by extending Michael Faraday's theories of electricity and magnetic lines of force. He then began to see the connections between the approaches of Faraday, Reimann and Gauss. As a result, he was able to derive one of the most elegant theories yet formulated. Using four equations, he described and quantified the relationships between electricity, magnetism and the propagation of electromagnetic waves. The equations are now known as Maxwell's Equations.
One of the first things that Maxwell did with the equations was to calculate the speed of an electromagnetic wave and found that the speed of an electromagnetic wave was almost identical to the speed of light. Based on this discovery, he was the first to propose that light was an electromagnetic wave. In 1862 Maxwell wrote:
This was a remarkable achievement, for it not only unifies the theories of electricity and magnetism, but of optics as well. Electricity, magnetism and light can now be understood as aspects of a single phenomenon: electromagnetic waves.
Maxwell also described the thermodynamic properties of gas molecules using statistical mechanics. His improvements to the kinetic theory of gases included showing that temperature and heat are caused only by molecular movement. Though Maxwell did not originate the kinetic theory, he was the first to apply probability and statistics to describe temperature changes at the molecular level. His theory is still widely used by scientists as a model for rarefied gases and plasmas.
Maxwell also contributed to the development of color photography. His analysis of color perception led to his invention of the trichromatic process. By using red, green and blue filters he created the first color photograph. The trichromatic process is the basis modern color photography.
Maxwell's particular gift was in applying mathematical reasoning in solving complex theoretical problems. Maxwell's Electromagnetic Equations are perfect examples of how mathematics can be used to provide relatively simple and elegant explanations of the complex mysteries of the universe. Richard Feynman wrote of Maxwell:
"From a long view of the history of mankind, seen from, say, ten thousand years from now, there can be little doubt that the most significant event of the nineteenth century will be judged as Maxwell's discovery of the laws of electrodynamics."
Maxwell continued his work at the Cavendish Laboratory until illness forced him to resign in 1879. He returned to Scotland and died soon afterwards. He was buried with little ceremony in a small churchyard in the village of Parton in Scotland.
Around 1700, Newton concluded that light was a group of particles (corpuscular theory). Around the same time, there were other scholars who thought that light might instead be a wave (wave theory). Light travels in a straight line, and therefore it was only natural for Newton to think of it as extremely small particles that are emitted by a light source and reflected by objects. The corpuscular theory, however, cannot explain wave-like light phenomena such as diffraction and interference. On the other hand, the wave theory cannot clarify why photons fly out of metal that is exposed to light (the phenomenon is called the photoelectric effect, which was discovered at the end of the 19th century). In this manner, the great physicists have continued to debate and demonstrate the true nature of light over the centuries.
Known for his Law of Universal Gravitation, English physicist Sir Isaac Newton (1643 to 1727) realized that light had frequency-like properties when he used a prism to split sunlight into its component colors. Nevertheless, he thought that light was a particle because the periphery of the shadows it created was extremely sharp and clear.
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