Once an experimental novelty, electricity is now an utterly indispensable part of modern life. Providing us with lighting, climate control, entertainment, and more, it’s hard to imagine life without it. To provide electrical power, energy is converted from other forms into electricity, powering the systems and devices we often take for granted.
Converting energy from one form to another is the key to understanding the differences between electric motors and generators. An electric motor converts electricity into mechanical energy, providing a power source for machinery. A generator does the opposite of this, converting mechanical energy into electricity.
Despite this significant difference in function, electric motors and electric generators are closely connected by their underlying mechanisms and fundamental structure. Both rely on an important law of physics: Faraday’s Law of Electromagnetic Induction.
Faraday’s Law of Electromagnetic Induction: The Relationship Between Electricity and Magnetism
Today, it’s well known that electricity and magnetism are two manifestations of a single fundamental force, called electromagnetism. Central to the universe as we know it, the electromagnetic force is thought to have existed in its current form since somewhere between 10^12 and 10^6 seconds after the Big Bang.
In 1831, physicist Michael Faraday discovered electromagnetic induction, revealing the intimate relationship between the observed phenomena of magnetism and electricity. Interestingly, in 1832, another researcher, Joseph Henry, discovered it independently. Faraday was the first to publish his findings, and to this day, he is credited with the discovery. Later, James Clerk Maxwell would discover a way to formulate Faraday’s findings mathematically, leading to the development of the Maxwell-Faraday equation.
Faraday’s Law of Induction is a law of physics designed to accurately predict and measure how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF). EMFs convert other forms of energy, such as mechanical energy, into electrical energy. This law of physics is what allows us to create both electric motors and electric generators. Although these two types of machinery perform opposite functions, they both rely on the same underlying laws of physics.
Electric Generators: Converting Mechanical Energy into Electric Energy
According to Faraday’s Law of Induction, whenever there is a change in the magnetic field across a conductor, such as a wire coil, electrons are forced to move perpendicular to that magnetic field. This generates electromotive force, which creates a flow of electrons in one direction. This phenomenon can be used to produce electricity in an electric generator.
To create this magnetic flux, the magnets, and the conductor is moved relative to one another. The wires are wound into tight coils, increasing the number of wires and the resulting electromotive force. By continuously rotating either the coil or the magnet, while keeping the other in place, gives continual flux variation. The rotating component is referred to as a “rotor,” while the stationary component is called a “stator.”
Electric generators fall into two broad categories: “dynamos,” which generate direct current, and “alternators,” which generate alternating current.
The dynamo was the first form of electric generator that was useful for industrial applications. During the Industrial Revolution, it was invented independently by several people. The electric dynamo uses rotating coils of wire and magnetic fields to convert mechanical energy into direct current (DC). Historically, dynamos were used for electric power generation, often using steam as a source to generate the needed mechanical energy.
Today, the electric dynamo has few uses outside of a few low-power applications. Alternators are far more widespread for electricity generation. This type of generator converts mechanical energy into alternating current. A rotating magnet serves as the rotor, turning within a set of conductor coils on an iron core, which serves as the stator. As the magnetic field rotates, it generates an AC voltage in the stator. The magnetic field can be created either by permanent magnets or by a field coil electromagnet.
An automobile’s alternator, as well as central power stations that provide electricity to a grid, are electric generators.
Electric Motors: From Electrical Energy to Mechanical Energy
An electric motor does the opposite of an electric generator. Instead of turning mechanical energy into electricity, an electric motor takes electricity and converts it into mechanical energy. Electric motors can be found in a diverse range of applications, from industrial manufacturing machinery to everyday household appliances. The rotor turns a shaft to create mechanical power. The stator is made from coil windings or permanent magnets, with a core of thin sheets layered together. Known as laminations, these layers create less energy loss than a solid core. Between the rotor and stator is a small air gap, which helps increase the magnetizing current.
Although electric motors can be piezoelectric, electrostatic, or magnetic, the vast majority of modern motors use magnets. Some are designed to run on DC, while others use AC. You can find electric motors of all sizes in an impressively wide range of applications. From tiny motors in battery-powered watches to massive electric motors that power industrial manufacturing machinery, this robust yet elegant piece of technology is central to modern life as we know it.
How the Discovery of a Fundamental Law of Physics Changed the World Forever
As we’ve mentioned, although electric motors and electric generators perform opposite functions, they both rely on the same underlying physical principle: Faraday’s Law of Induction. During the early nineteenth century, Michael Faraday’s contributions to the study of electricity and magnetism were unparalleled. Despite having little formal education, and despite the fact that the empirical study of physical phenomena was a relatively new field of knowledge, Faraday is without a doubt one of the most influential scientists in all of human history.
Faraday’s monumental discovery– that magnetic fields interact with electric currents to create an electromotive force — opened the door to the modern electric technology that we take for granted today. Faraday’s law of induction is the principle behind transformers, electric motors, electric generators, inductors, and solenoids. Without this knowledge, we would not have been able to develop reliable equipment for generating electricity to the grid. We also wouldn’t have electric motors to power other machinery. In fact, the electrodynamics developed by Faraday and later Maxwell were also a major catalyst for Albert Einstein’s theory of Special Relativity.
Electric motors and electric generators, regarding their function, are quite distinct from one another. But ultimately, they exemplify two sides of the same coin. Both rely on the same underlying physical principles, and understanding those principles has been instrumental in the development of even the most commonplace modern technology.
(Editor’s Note: This post was originally published in July 2012 and has been completely revamped and updated for accuracy and comprehensiveness.)