Question

What is the phase relationship between the current and voltage in an RC circuit?

Answer 1

In an RC circuit (Resistor-Capacitor circuit), the phase relationship between the current and voltage depends on the frequency of the applied voltage signal.

At low frequencies:
When a low-frequency voltage signal is applied to an RC circuit, the capacitor has enough time to charge and discharge fully between each cycle of the signal. In this case, the phase difference between the current and voltage is zero, meaning they are in phase with each other. Both the current and voltage waveforms reach their maximum and minimum values at the same time.

At high frequencies:
As the frequency of the applied voltage signal increases, the time available for the capacitor to charge and discharge decreases. When the frequency becomes significantly high, the capacitor cannot fully charge or discharge during each cycle. As a result, the capacitor begins to act as a reactance and impedes the flow of current, causing the current to lag behind the voltage.

In this high-frequency scenario, the current lags behind the voltage, and the phase difference between them becomes 90 degrees. The voltage reaches its peak value before the current does.

So, in summary:

At low frequencies, the current and voltage are in phase (0 degrees phase difference).
At high frequencies, the current lags behind the voltage by 90 degrees.