Electromagnetic induction

Figure 1. One of Michael Faraday's first devices for demonstrating induction.[1]

Electromagnetic induction is the production of an electromotive force (EMF) being created as a result of relative motion between a magnetic field and a conductor. It was discovered in 1831 by Michael Faraday,[2] and lays the foundation for electrical generation in power plants, electric motors, and AC circuitry which powers the electrical grid, transformers, and many more phenomena.

The equation that mathematically describes electromagnetic induction is Faraday's Law, which states that any change in the magnetic environment of a coiled wire will cause a voltage (EMF) to be induced.[3] Faraday found many ways for this to happen such as changing the magnetic field strength, moving a magnet through a coil of wire, and moving the coil through a magnetic field, just to name a few. The voltage (EMF) generated in a coil of wire can be described by the following equation:[3]

[math]EMF=-N\frac{\Delta(BA)}{\Delta t}[/math]


  • [math]N[/math] is the number of turns in the wire
  • [math]\Delta(BA)[/math] is the change in magnetic flux
  • [math]\Delta t[/math] is the change in time

The ways that Faraday found to change this flux as stated above can all be represented in this equation. The reason this equation is negative is because of Lenz's law, which requires any change in magnetic flux to be reproduced in equal strength but opposite direction by the wire.

Faraday's law is important for many electromagnetic applications in the world, including cars. The ignition system in a car's internal combustion engine takes only 12 volts from the battery and ramps that up to 40000 volts! Visit Hyperphysics to learn how.

PhET Simulation of Induction

PhET has graciously allowed us to use their simulations, and the one below demonstrates Faraday's law of electromagnetic induction. The voltage is seen to change as the magnetic flux changes through it.

For Further Reading

For further information please see the related pages below:


  1. Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/1/19/Faraday_disk_generator.jpg
  2. UIUC Physics, A Brief History of The Development of Classical Electrodynamics [Online PDF], Available: http://web.hep.uiuc.edu/home/serrede/P435/Lecture_Notes/A_Brief_History_of_Electromagnetism.pdf
  3. 3.0 3.1 Hyperphysics, Faraday's Law [Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html