When the magnetic flux through the coil is made to vary, an emf is induced in the coil. The magnitude of the induced emf is proportional to the rate of change of flux.
Hence, E ∝ dΦ/dt where dΦ = Change in flux/dt =time taken to change
The emf is also dependent on the number of turns on the coil (N), the greater the number of turns on the coil, the greater emf. Hence, we may write:
E ∝ N dΦ/dt Volts