In physics, the Faraday effect or Faraday rotation is a magneto-optical phenomenon, or an interaction between light and magnetic field in a medium. The rotation of the plane of polarization is proportional to the intensity of the component of the magnetic field in the direction of the beam of light.The Faraday effect, discovered by Michael Faraday in 1845, was the first experimental evidence that light and electromagnetism are related. The theoretical basis for that relation, now called electromagnetic radiation, was further developed by James Clerk Maxwell in the 1860s and 1870s. This effect occurs in most optically transparent dielectric materials (including liquids) when they are subject to strong magnetic fields.