How can one distinguish a capacitor for a DC circuit from one for an AC circuit?

The ability to distinguish a capacitor for a DC circuit from one for an AC circuit primarily comes down to the presence of polarity markings. In general, electrolytic capacitors, which are often used for DC applications, have polarity and must be connected in the correct direction to function properly. These capacitors usually have a negative and positive terminal marked to indicate how they should be connected in a circuit.

In contrast, non-polarized capacitors, such as ceramic or film capacitors, can be used in AC applications because they do not have a polarity and can be connected in either direction. This characteristic is particularly important because applying DC voltage to a non-polarized capacitor can lead to failure, while using a polarized capacitor in an AC application could damage the capacitor and the circuit.

While checking the size or voltage rating of capacitors can provide information about their specifications, these factors are not definitive indicators of their intended usage in AC versus DC circuits. Measuring capacitance similarly does not reveal the polarity characteristics necessary to distinguish the types of capacitors effectively. Therefore, recognizing the polarity markings is the most reliable method for identifying whether a capacitor is suited for DC or AC applications.