RC Circuit

Definition: The combination of a pure resistance R in ohms and pure capacitance C in Farads is called RC circuit. It is also called first order RC circuit and is used to filter the signals by passing some frequencies and blocking other.

RC Series Circuit

A circuit containing resistance and capacitance connected in series together is called an RC series circuit.

circuit diagram of RC Series circuit

Steps to draw a phasor diagram for an RC circuit

  1. Current I is taken as reference
  2. Voltage drop in resistance is (VR). 

         VR = IR is drawn in phase with the current I

  1. Voltage drop in capacitive reactance is (VC).

         VC = IXC  and  is drawn 90° behind the current (as current leads the voltage

by 90° in pure capacitive load circuit).

  1. The vector sum of the two voltage drops is equal to the applied voltage (V).

phasor diagram of RC Series circuit
RC-CKT-EQ-1

Now in right angle triangle OMN

V = √(VR)2+(VC)2

V =  √(IR) 2 + (IXC) 2

V = I  √R2 + X2C

I = V/√R2 +X2C  = V/Z

Where Z= √R2 +X2C

Z is known as impedance of the circuit and is defined as the total opposition offered to the flow of current in an RC series circuit. It is measured in ohms.

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