The magnetic flux through a surface of area A placed in a uniform magnetic field B is defined as, ΦB = B.A = BA cos θ where θ is the angle between B and A.
Faraday’s laws of induction imply that the emf induced in a coil of N turns is directly related to the rate of change of flux through it.
Lenz’s law states that the polarity of the induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produces it. The negative sign in the expression for Faraday’s law indicates this fact.
When a metal rod of length l is placed normal to a uniform magnetic field B and moved with a velocity v perpendicular to the field, the induced emf (called motional emf) across its ends is ε = Blv.
Changing magnetic fields can set up current loops in nearby metal (any conductor) bodies. They dissipate electrical energy as heat. Such currents are eddy currents.
Inductance is the ratio of the flux-linkage to current. It is equal to NΦ/I.
In an ac generator, mechanical energy is converted to electrical energy by virtue of electromagnetic induction.