Electronics Engineering (ELEX) Board Practice Exam

What describes the behavior of a capacitor in AC circuits?

1. It blocks DC but allows AC

2. It easily passes both AC and DC

3. It blocks AC but allows DC

4. It stores energy only in AC circuits

The correct answer is: It blocks DC but allows AC

The behavior of a capacitor in AC circuits is accurately described by the assertion that it blocks DC but allows AC to pass through. This characteristic stems from the fundamental workings of capacitors. In DC circuits, once a capacitor becomes fully charged, it presents an open circuit condition, effectively blocking any further flow of direct current. However, when alternating current is applied to a capacitor, the voltage across the capacitor continuously changes polarity. This ongoing change allows the capacitor to charge and discharge periodically, resulting in the effective passage of AC current. Thus, capacitors are commonly used in AC applications for coupling and filtering purposes, taking advantage of their ability to allow AC signals to pass while preventing DC signals from traveling through. This principle is crucial in designing circuits that require signal processing or power management in AC systems.