RC Circuit acts as a Resistor and Capacitor and Common Applications

RC Circuit:

When a resistor and a capacitor are connected in series with a ac voltage source, then it is called series RC circuit. It is a first order differential circuit.  In this circuit, the values of R , C and applied voltage are fixed. By varying the frequency of the applied voltage, this RC circuit acts as a resistive circuit and capacitive circuit.

RC circuit

Fig : - RC circuit



Total impedance of the circuit  Z  = sqr(R2  + Xc2)

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

RC circuit acting as a capacitor: 

As we know that, Capacitive reactance, Xc = 1 / 2πfC,  that is capacitive reactance decrease with increasing signal frequency.

So at low frequency, the RC circuit acts as a capacitive circuit, because at low frequency, capacitive reactance will be much much greater than the resistance. And the circuit will act as a capacitor and shows all the properties that a capacitor can show. i.e

     1. This circuit will store energy in the form of electric charge.
    2.  Phase shift between voltage and current will be 90 degree
    3. Current will lead voltage by 90 degree.
Phase shift , acting as a capacitor

Fig-2 : Phase shift of a RC circuit acting as a capacitor at low frequency


RC circuit acting as a resistor: 

At high frequency , Capacitive reactance , Xc will be low than the resistance, and the whole 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 .


Phase shift, RC circuit, resistor

Fig -3: Phase shift of a RC circuit acting as a resistor at high frequency



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

Common Applications of RC circuit :

These are some common application of RC circuit

1. Low pass filter
2. High pass filter
3. Notch filter
4. Phase shift Oscillator
5. Determine in time constant etc

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