When an emf is generated by a change in magnetic flux according to Faraday’* Law the polarity of the induced emf is given by Len'z Law.
Len'z Law:
The direction of induced emf in the coil or conductor is such as to oppose the change in magnetic flux which produces it.
E = - (dΦ/dt)
- Ve sign indicates that the induced e.m.f opposes the change in the magnetic flux.
The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
