Which capacitor is polarized, making it unsuitable for AC?

• A. Electrolytic capacitor
• B. Ceramic capacitor
• C. Film capacitor
• D. Mica capacitor

Answer: (A)

Capacitors that are polarized have a definite positive and negative lead and must be connected with the correct polarity. The dielectric in these devices relies on an oxide layer formed by the metal electrode, which is stable only in one direction. When reverse polarity is applied, this oxide can break down, causing leakage, heating, and often venting or failure. Because AC continually reverses polarity, a polarized capacitor would experience reverse bias with each half-cycle, making it unsuitable for AC signals or AC-coupled circuits. Electrolytic capacitors are the classic polarized type, offering high capacitance in a compact package, but they must be biased correctly and are vulnerable to reverse voltage. The other listed capacitors—ceramic, film, and mica—are non-polarized, so they tolerate reverse voltage and are appropriate for AC applications and bidirectional signals. In practice, use electrolytics for DC purposes with fixed polarity, and choose ceramic, film, or mica capacitors when the circuit involves AC or where polarity could reverse.