Faraday's law states that changing a magnetic flux produce an induced electromotive force:

E.M.F. = - d Φ/ d t ……………………. (6-5)

Where E.M.F. = electromotive force

d Φ = change of magnetic flux

d t = time of changing magnetic flux

The minus sign means that the direction of the induced electromotive force opposes the change of magnetic flux.