Faraday's law of induction makes use of the magnetic flux Φ B through a region of space enclosed by a wire loop. The magnetic flux is defined by a surface integral : Φ Φ B = ∫ ∫ Σ Σ B ⋅ ⋅ d A , where d A is an element of the surface Σ enclosed by the wire loop, B is the magnetic field. The dot product B · d A corresponds to an infinitesimal amount of magnetic flux. In more visual terms, the magnetic flux through the wire loop is proportional to the number of magnetic field lines that pass through the loop.