Consider fig 11-1 The element dl moves at the velocity v The product r da dt dl=(dr×dlt dt where da= dr x dl is the area swept by the element dl over a small displacement dr
Thus da d更 =-B dt dt where qp is the magnetic flux passing through the closed path C, and dq is its variance caused by the displacement dr The direction of y is determined as follows V drives the current that generates a magnetic field in the opposite direction to the increase of the orig- inal B 一 The Faraday Law for v× B field