During the first five time cunstants, the current is building up exponentially, and the induced coil voltage is decreasing. The resistor voltage increases with the current, as Figure 11-24(c) illustrates. After five time constants have elapsed, the current has reached its final value, VS/R. At this time, all of the source voltage is dropped across the resistor and none across the coil. Thus, the inductor effectively acts as a short to non-changing current, as Figure 11-24(d) illustrates. Keep in mind that the inductor always change in current.
Now let’s examine the case illustrated in Figure 11-25 where the current is switched off, and the inductor discharges through another path. Part (a) shows the steady-state condition, and part (b) illustrates the instant at which the source is removed by opening SW1 and the discharge path is connected by the closure of SW2. There was 1 A thorough the inductor prior to this. Notice that 10 V are induced in the inductor in the direction to aid the 1 A in an effort to keep it from changing. Then as shown in Figure 11-25(c), the current decays exponentially, and so do VR and V1 After 5T, as shown in Figure 11-25(d), all the energy stored in the magnetic field of the inductor is dissipated, and all values are Zero.