Electromagnetic induction

(a) An e.m.f. is induced in a coil if the magnetic flux through the coil changes (b) The magnitude of the induced e.m.f. depends on (i) the rate of change of flux (ii) the number of turns on the coil (iii) the cross-sectional area of the coil The faster the flux is changed the greater is the e.m.f. produced.

The e.m.f (E) generated in the coil is given by the formula:

E=-d(NF)/dt = -NdF/dt

where N is the number of turns in the coil and F the magnetic flux through one coil.
Magnetic flux is a measurement of the ‘amount’ of magnetism. (See magnetic flux density). In a way it is the ‘flow’ of magnetic field through the coil.
The quantity NF is known as the flux linkage and is measured in webers.
The quantity d(NF)/dt is the rate of change of flux linkage in webers per second.

This change of flux can be produced by either:
(a) moving the wire or coil through the field
(b) changing the intensity of the magnetic field