V=L x di/dt is a well known formula used to calculate the voltage across an inductor due to a collapsing magnetic field. It seems to me that the formula could also be arranged to say: V = i x dL/dt Voltage is equal to current times the change in inductance... If this formula is true would a decreasing (collapsing) inductance produce an opposite polarity across the coil than an increasing inductance? if I wind two coils together and connect them in a series circuit so they oppose each other. When the pulse goes through the coils it would cause the inductance to change (drop to zero) and induce a voltage across the coil? Could the equation above then be used to calculate the voltage across the coil? Are there any applications where this is used?