# Current in a RC circuit

In order to find current in an RC circuit, resistance of only the resistor is considered i.e. $$I_\text{resistor} = V_\text{resistor} / R$$. Why is the reactance of the capacitor not considered? The frequency of the ac signal has an affect in circuit with a capacitor. Why is that effect is not considered while calculating current in a RC circuit?

• "In order to find current in RC circuit, resistance of only resistor is considered" - This isn't true. – Alfred Centauri Jan 23 '18 at 13:05
• Looking closely at what you wrote, I see that it is can be true depending on how the circuit is wired, and what you mean by "current in RC circuit". But it is not particularly useful. The current in the resistor is indeed Voltage(resistor)/Resistance(resistor), but this may not be "current in RC circuit". – garyp Jan 23 '18 at 13:53
• Do you mean an RC series connected to a DC source? The voltage across the resistor is affected by the voltage across the capacitor. And you have the concept backwards. The capacitive reactance is an effect built from the basic behavior of the capacitor, $Q=CV_C$. – Bill N Jan 23 '18 at 13:56

## 2 Answers

No.both are considered to find the current let the alternating voltage varies in sinusoidal form the current is given by the voltage equation (sinusoidal form with phase change as there is phase difference between the impedance vector and the resistance) divided by impedance(which involves both resistance and capacitive reactance.

Capacitive reactance is a description of behaviour of capacitor in AC circuits, where current oscillates harmonically and all transient phenomena in the circuit died away long time ago.

In case we study discharge of the capacitor through a resistor, there is no AC current, just a transient discharge. The discharge requires more detailed description in terms of differential equation in time, the concept of impedance or reactance is not applicable.