Consider an RL circuit consisting of a resistor, an inductor, a constant source of emf, and switches S1 and S2. When switch S1 is closed, the current in the circuit increases, generating emf across the resistor and inductor. These emf's are used in Kirchhoff's loop rule to find the current growth rate. On rearranging and integrating the equation, the current in the RL circuit with emf is obtained. After attaining the steady state, switch S2 is closed while S1 is opened, forming a single loop bypassing the emf source. This results in current decay through the resistor and inductor. The decayed current is obtained using Kirchhoff's rule. The quantity inductance over resistance is called the inductive time constant. The current versus time graph shows that, when time equals time constant, the current grows to 63 percent of its final value, whereas during decaying, at the same value of the time constant, the current decays to 37 percent of its original value. Hence, the current increases gradually from zero to a steady state but decays exponentially with time.