Introduction: RC Circuits
- Impedance: is what the source “Sees” as total Opposition to Current.
The method of calculation of impedance differs from one circuit
When a circuit is purely capacitive(contains capacitor only), the phase angle between applied voltage and total current is 90 ° (Current Leads)
- When there is a combination of both resistance and capacitance in a circuit, the phase angle between resistance (R) and capacitive reactance (XC ) is 90 ° and the phase angle for total impedance (Z) is somewhere between 0 ° and 90 °.
- When there is a combination of both resistance and capacitance in a circuit, the phase angle between total current (I T) and the capacitor voltage (V C) is 90 ° and the phase angle between the applied voltage (VS ) and total current (I T ) is somewhere between 0 ° and 90 ° , depending on relative values of resistance and capacitance.
Step 3: Voltage and Current Phasor Diagram for the Waveforms
Step 4: Current, Resistance and Voltage Phase Angles of Series RC Circuits
Step 5: Impedance and Phase Angle of Series RC Circuits
- In the series RC circuit, the total impedance is the phasor sum of R and Xc
- Impedance magnitude: Z = √ R^2 + Xc^2 (Vector sum)
- Phase angle: θ = tan-1(X C/R)
Why do we use vector sum not algebraic sum ?
Ans: Because Resistance doesn’t delay the voltage, but the Capacitor do that.
So, Z=R+Xc is wrong.
- The application of Ohm’s law to an entire series RC circuit involves the use of the quantities Z, Vs, and Itot as:
Also don’t forget:
Step 6: Variation of Impedance With Frequency
Step 7: Variation of Impedance and Phase Angle With Frequency
Step 8: An Illustration of How Z and XC Change With Frequency
R remains constant