Since the charge depends only on the total change in magnetic flux during the time, and not any instantaneous result, we can apply Felici's law to measure the magnetic flux and thus a constant magnetic field. In the flip-coil method, we wind 'n' overlapping loops in a small ring. We first insert the coil perpendicular to the field and then rotate it 180°. Thus the end magnetic flux is exactly opposite the initial flux since the magnetic field is constant. By Felici's law, for area A and resistance R, we can find the magnetic field B