The magnitude of an electromagnetically induced e.m.f. (E) is given by E=−dΦ‎/dt, where Φ‎ is the magnetic flux. This is a quantitative statement of Faraday’s second law of electromagnetic induction and is sometimes known as the Faraday–Neumann law. This law was stated quantitatively by the German physicist Franz Neumann (1798–1895) in the 1840s.