Question

For which frequency range (high or low) does the RC circuit on the left act like the circuit on the right? Briefly explain.

Answer 1

At low frequencies RC circuit on the left acts like right circuit.

Impedance of a Capacitor is

     $-\frac{j}{\omega c}$        Where

                        c is capacitance of the capacitor.

                        $\omega = 2\pi f$    where f is frequency.

So, the Impedance of the Capacitor is $-\frac{j}{2\pi f c}$

For Low frequencies or DC f is low or zero i.e. Impedance of the Capacitor is infinite. So resistance can be ignored and only capacitor exists. And it acts like a open circuit.

For high frequencies, f is high and Impedance of Capacitor is almost equal to zero. And Capacitor behaves like short circuit and only resistor exists.