Figure 19.14 An RL circuit.Imagine that we connect the switch in the circuit in Figure 19.15 at time t = 0. At that point, the current
will change rapidly from zero to some nonzero value. So, because is large, the inductor has a large
voltage drop, the resistor has very little voltage drop, and the current cannot immediately reach its
maximum value. After a while, though, the current changes less rapidly, the voltage drop across the
inductor becomes small, the voltage drop across the resistor gets bigger, and the current in the circuit
becomes large.
A graph of current vs. time for this circuit is shown in Figure 19.15 .
Figure 19.15 Graph of current vs. time for a simple RL circuit.What would happen if we disconnected the battery? Well, the inductor would discharge its energy through
the resistor. At first, the inductor would resist the decrease in current; but after a long time, the current
would reach zero, as shown in Figure 19.16 .
Figure 19.16 Graph of current vs. time for a simple RL circuit once the battery is disconnected.