IN Section 3-11 we discussed the fact that work is required to assemble a group of charges and that the work is stored as electric energy. We certainly expect that work also needs to be expended in sending currents into conducting loops and that it will be stored ass magnetic energy. Consider a single closed loops with a self inductance L1 in which the current is initially zero. A current generator is connected to the loop, Which increases the current i1 from zero to I1. From physics we know that an electromotive force (emf) will be induced in the loop that opposes the current change. An amount of work must be done to overcome this induced emf. Let V1=L1di/dt be the voltage across the inductance. The work required is