Electromagnetic induction is the production of voltage across a conductor when it is exposed to a changing magnetic field. Discovered by Michael Faraday in 1831, this phenomenon forms the basis of generators, transformers, and many electrical devices we use today. In this demonstration, we have a coil of wire connected to an ammeter, and a magnet nearby. When the magnet remains stationary, no current flows through the circuit. However, when the magnet moves toward or away from the coil, the changing magnetic field induces a voltage in the coil, causing current to flow through the circuit.
Faraday's Law of Electromagnetic Induction states that the induced electromotive force, or EMF, in a circuit is directly proportional to the rate of change of magnetic flux through the circuit. Mathematically, this is expressed as E equals negative d-phi-B over dt, where E is the electromotive force, phi-B is the magnetic flux, and the negative sign represents Lenz's Law. In this graph, the blue curve represents the magnetic flux changing over time, while the red curve shows the induced EMF. Notice that when the flux is changing rapidly, either increasing or decreasing, the magnitude of the induced EMF is large. When the flux change is slow, the induced EMF is small. And when the flux reaches its maximum or minimum points, where the rate of change is zero, the induced EMF is also zero.
Lenz's Law is a key principle in electromagnetic induction. It states that the direction of the induced current is such that it creates a magnetic field that opposes the change in magnetic flux that produced it. This is represented by the negative sign in Faraday's Law and is a consequence of the conservation of energy. Let's see this in action. When a magnet moves toward a coil, the magnetic flux through the coil increases. According to Lenz's Law, the induced current in the coil will create its own magnetic field that opposes this increase in flux. This means the induced magnetic field will repel the approaching magnet, creating a force that opposes the motion of the magnet. This opposition is why work must be done to move the magnet, which is then converted into electrical energy in the coil. Without this opposition, we would violate the conservation of energy by creating energy from nothing.
Electromagnetic induction has numerous practical applications in our modern world. One of the most important is the electric generator, which converts mechanical energy into electrical energy. In a generator, a coil of wire rotates within a magnetic field. As the coil rotates, the magnetic flux through it changes, inducing an alternating current. This is the fundamental principle behind power generation in hydroelectric dams, wind turbines, and thermal power plants. Another crucial application is the transformer, which uses mutual induction between two coils to transfer electrical energy and change voltage levels. This is essential for efficient power transmission over long distances. Induction motors are also based on electromagnetic induction, using rotating magnetic fields to induce currents in a rotor, creating mechanical motion. These motors power everything from industrial machinery to household appliances.
Let's summarize the key concepts of electromagnetic induction. First, electromagnetic induction is the production of voltage across a conductor when it is exposed to a changing magnetic field. Second, according to Faraday's Law, the induced electromotive force is directly proportional to the rate of change of magnetic flux through the circuit. Third, Lenz's Law tells us that the induced current creates a magnetic field that opposes the change that produced it, which is a consequence of the conservation of energy. Fourth, this phenomenon has numerous practical applications, including electric generators, transformers, induction motors, and wireless charging technologies. Finally, electromagnetic induction is fundamental to modern electrical power generation and distribution systems, making it one of the most important discoveries in the history of physics and engineering. Without it, our modern electrical world would not exist.