31.9: Comparison between RL and RC circuits
An RC circuit consists of resistance and capacitance, while in an RL circuit, capacitance is replaced by an inductor. RL and RC circuits are first-order differential circuits that store energy. An RC circuit stores energy in the electric field, while an RL circuit stores energy in the magnetic field. When connected to a battery, an RC circuit charges the capacitor, causing the current to decrease from maximum to zero upon being fully charged. This increases the voltage across the capacitor from zero at the uncharged state to maximum at the fully charged state.
On the other hand, in an RL circuit, on connecting the battery, current flows in the circuit, producing an emf across the inductor. By Lenz's law, the induced emf of opposite polarity counteracts the increase in the circuit's current. As a result, the current starts at zero and increases asymptotically to its final value. This decreases the voltage across the inductor from a maximum value to zero.
Both RC and RL circuits can dissipate energy through Joule heating in the resistance of the circuit. In an RC circuit, the current flows in the opposite direction during discharging compared to when it charges, and its magnitude increases with time. This causes the voltage to drop across the capacitor from a maximum value to zero. Whereas, during discharging of inductor in an RL circuit, an exponential decrease in current and a rise in voltage across the inductor is observed.
Both RC and RL circuits are the backbone of electronic circuits. Both have their merits and demerits. An RC circuit is useful in dealing with low-power applications, while RL circuits are more complex and can be used in high-power applications.