Question

Under what condition rc circuit behaves like a low pass filter

Answer 1

First you need to understand the underlying logic of how the filters work. Before that, understand how a capacitor works when an input voltage having a certain frequency is applied to it.

Lower Frequencies:In lower frequencies, during one half of the cycle, the plates of the capacitor get enough time to get charged up. The potential drop across the capacitor is nearly equal to that of the peak of the applied input voltage. After the capacitor is charged up, it behaves like an open circuit to current. So appearntly, all the voltage drop is across the capacitor in the circuit.

Higher frequencies: In Higher frequencies, the capacitor doesn’t get enough time to get charged up and before it could get charged completely, the negative cycle is already applied across it and the potential drop is very little compared to the lower frequency case.

This is the main logic behind a passive filter. Before explaining the working, let’s have a look of the two filters,