NEIEP Mechanics Practice Exam

What occurs in a circuit when the capacitor voltage equals the source voltage?

1. Resistance increases

2. Current flow stops

3. Voltage increases

4. Capacitance fails

The correct answer is: Current flow stops

When the voltage across a capacitor reaches the same level as the source voltage in the circuit, the current flow stops. This phenomenon is due to the nature of capacitors, which store electrical energy in an electric field. Initially, when a capacitor is uncharged and a voltage is applied, current flows into the capacitor to charge it. As the capacitor charges, the voltage across it increases. Once the capacitor's voltage equals the source voltage, the potential difference that drives the current flow ceases to exist, leading to a stop in current flow. This concept is fundamental in understanding how capacitors operate in various circuits, particularly in DC circuits, where they can become fully charged and effectively act as open circuits.