Faraday’s Law


Faraday’s law or also called the law of electromagnetic induction, is a postulate based on the experiments of Michael Faraday, a British physicist who in 1831 stated that the voltage that develops in a closed circuit is openly proportional to the speed with that is modified in time, the magnetic circulation that penetrates all kinds of surfaces with the circuit as an edge.

Faraday’s law is a fundamental correlation that was worked out based on Maxwell’s equations. It can be used as a condensed summary of the ways in which a voltage can be created, through changing the magnetic environment. The voltage induced in a coil is equivalent to the negative of the rate of change of the magnetic flux multiplied by the number of turns of the coil, which causes the charge to interact with the magnetic field.

It should be noted that the most important experiment that prompted Faraday to create his law was extremely simple. Faraday used a cardboard cylinder, with a wire wrapped around it to create a coil. He linked a voltmeter across the coil and recorded the voltage induced as a magnet passed through the coil.

This experiment led him to the following conclusions:

  • While the magnet was at rest or close to the coil: no voltage was felt.
  • When the magnet was entering the coil: there was a small voltage record, which reached a very high magnitude, when the magnet was very close to the center of the coil.
  • When the magnet is passing through the center of the coil: a sudden change in voltage sign was noted.
  • When the magnet started to move out of the coil: A reverse voltage was noted in the opposite orientation of the magnet moving towards the coil.

All these observations are highly consistent with what is stated in Faraday’s law. Even when the magnet is at rest, it is capable of creating a tremendous magnetic field without inducing any voltage, since the flux through the coil is unchanged. As the magnet approaches the coil, the flux increases sharply, until the magnet is located inside the coil. Once it passes through it, the magnetic flux begins to descend. Subsequently, the induced voltage is reversed.