R-L Circuit

Series R-L Circuit:

An a.c. circuit containing an inductor and a resistor connected in series is called an R-L Series Circuit .

A typical R-L circuit is shown in the diagram below:

Series R-L Circuit Phasor (Vector) Diagram:

• The reference vector is labelled I  and represents the current in the circuit, which is common to all circuit elements.

• The inductor voltage V_L  leads the current by \( \frac {\pi}{2 } \scriptsize \; or \; 90^{\circ}\)and is drawn leading the current vector by 90 degrees, as represented by the red line in the phasor diagram.

• In a resistor, the current through the resistor remains in phase with the voltage drop across it, as represented by the green line in the phasor diagram shown above.

• The phase shift between the applied voltage and current is between 0 and 90 degrees. From the phasor diagram, it is clear that in an R-L series circuit, the current always lags the voltage by an angle Φ