RL Circuit acts as a resistor and Inductor and Common Application in Practical Life

RL Circuit:

When a resistor (R) and a inductor (L) are connected in series with a ac voltage source (v), then it is called series RL circuit. It is a first order differential circuit.  In this circuit, the values of R , L and v are fixed. By varying the frequency of the applied voltage, this RL circuit acts as a resistive circuit and inductive circuit.

Fig-1: RL Circuit

Total impedance of the circuit  Z  = sqr(R²  + X_L²)

From the above equation we see that , total impedance of a RL circuit consist of resistance and inductive reactance. The total impedance changes with frequency.

 RL circuit acting as a Resistor: 

As we know that, Inductive reactance, X_L =  2πfL,  that is inductive reactance increases  with increasing signal frequency.

So at low frequency, the RL circuit acts as a resistive circuit, because at low frequency, inductive reactance will be much much lower than the resistance. And the circuit will act as a resistor and shows all the properties that a resistor can show. i.e

1.     The circuit will loss energy or convert energy as a form of heat.

2.     Phase shift between voltage and current will be zero .

RC circuit acting as a Inductor: 

At high frequency , Inductive reactance , X_L will be high than the resistance, and the whole circuit will act as a inductor and shows all the properties that a inductor can show. i.e

1.     This circuit will store energy in the form of magnetic flux.

2.     Phase shift between voltage and current will be 90 degree

3.     Voltage will lead current by 90 degree.

 

Fig-2: Phase Shift of a RL Circuit

So , just by changing signal frequency , we can convert  a RL circuit as a resistive circuit  and Inductive  circuit.

Common Applications of RL circuit :

These are some common application of RL circuit

1. Low pass filter

2. High pass filter

3. Notch filter

5. Determine in time constant etc