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Electromagnetism is the fundamental force that describes the relationship between electricity and magnetism. Maxwell’s equations quantify the basic principles of electromagnetic theory, which revolutionized the way physicists understood light. The success of electromagnetic theory led to the collapse of Newtonian physics and altered the way physicists understand electricity, magnetism, light, space, time, and gravity.
Einstein’s theory of special relativity describes magnetism as the byproduct of the electric force. Thus, these two forces can be considered different facets of a more fundamental force, which physicists call electromagnetism. Electromagnetic theory describes a collection of interconnected scientific statements used to answer questions about this force.
Physicists use fields as abstractions to describe how a system affects its surroundings. The electric field of a charged object represents the force it would exert on a charged particle. The field is stronger closer to the object because the electrostatic force decreases as the distance between two charges increases. Magnetic fields are defined similarly, except that they describe the force exerted on a charged particle in motion.
The most basic ideas in electromagnetic theory are “a changing electric field generates a magnetic field” and “a changing magnetic field generates an electric field”. These principles are quantified by Maxwell’s equations, named after James Clerk Maxwell, the Scottish physicist and mathematician whose 19th-century work established the discipline and revolutionized the way physicists understood light. Maxwell’s equations also throw previously known relationships – Coulomb’s law and Biot-Savart’s law – into the language of fields.
A charged particle generates a magnetic field as it moves, but the magnetic field is perpendicular to the motion of the particle. Furthermore, the effect this magnetic field has on a moving second charge is perpendicular to both the field and the motion of the second charge. These two facts mean that even basic problems in electromagnetism require complex, three-dimensional reasoning. Historically, the development of vectors in mathematics and science owes much of its progress to the work of physicists seeking to abstract and simplify the use of electromagnetic theory.
In the 19th century, electromagnetic theory changed the way physicists understood light. Newton had described light in terms of particles called corpuscles, but Maxwell argued that it was the manifestation of electric and magnetic fields that push each other through space. According to this view, visible light, x-rays, radar, and many other phenomena are all intrinsically similar, each a combination of electric and magnetic fields that vary at a different frequency. Scientists call the continuum of all these waves the electromagnetic spectrum.
The success of electromagnetic theory led to the collapse of the rest of Newtonian physics in the 20th century. Einstein realized that Maxwell’s theory required space and time at different, interdependent coordinates of a four-dimensional space-time. Furthermore, Einstein’s theory of relativity showed that space was curved and the passage of time measured by one observer differed from that measured by another. These discoveries were all completely incompatible with Newton’s theory of motion. Thus, the study of electromagnetism has, directly or indirectly, altered the way physicists understand electricity, magnetism, light, space, time, and gravity.
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