Lenz's law
The induced emf and the resulting induced current are counterclockwise when B' is directed out from the page and the area of the circuit is decreasing. The flux through this circuit is decreasing in the outward direction. Now the induced current I produces its own magnetic field, and we may use the right-hand grip rule to compute the direction of this field. The result is that the magnetic field due to the induced current is also directed outward within the circuit. It is as though nature, through this induced field, tried to compensate for the reduction in the flux due to the applied field B. This turns out experimentally to be a general rule, so that we may say thatThe direction of the induced emf is always such as to result in opposition to the change producing it.That is Lenz's law.