Series LR Circuit - Practice Questions & MCQ

Series LR circuit-

The above figure shows that pure inductor of inductance L connected in series with a resistor of resistance R through sinusoidal voltage, which is given by -  .

The alternating current I, which is flowing in the circuit gives rise to voltage drop V_R across the resistor and voltage drop V_L across the coil. As we have studied in previous concept that the voltage drop V_R across R would be in phase with current but voltage drop across the inductor will lead the current by a phase factor π/2.

So, the voltage drop across R is - V_R=IR

voltage drop across the inductor L is - 

Where, I is the value of current in the circuit at a given instant of time

So, the voltage phasor diagram is - 

In the above figure, we have taken current as a reference quantity because same amount of current flows through both the components. Thus from phasor diagram - 

Here, Z is known as Impedence of the circuit.

By using the formula of impedence we can write that - 

This is current in steady state which lags behind applied voltage by an angle φ.

From here and the above figure, we can write that - 

Important term - 

1. Power factor - 

                  resistance

                  impedence

2. Inductive susceptance () - 

It is the reciprocal of reactance.