RC Circuit

Definition: The combination of a pure resistance R in ohms and pure capacitance C in Farads is called RC circuit. The capacitor store energy and the resistor connect in series with the capacitor control the charging and discharging of a capacitor.The RC circuit is used in camera flashes, pacemaker, timing circuit etc.

The RC signal filters the signals by blocking some frequencies and allowing others to pass through it. It is also called first order RC circuit and is used to filter the signals by passing some frequencies and blocking others.The RC fitlers are mostly use for selecting signals and for rejecting noise.

The high-pass filter and the low-pass filter are the most common type of RC filters.The high pass filter passes the frequency greater than the fixed cutoff frequency and blocks the frequency lower than the fixed cutoff frequency. Similarly, the low-pass filter allows the frequency lower than the fixed cutoff frequency and attenuates the frequency higher than the fixed cutoff frequency.

RC Series Circuit

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

circuit diagram of RC Series circuitSteps 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 the 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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