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

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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