What type of current does a filter device primarily work on?

A filter device primarily works on alternating current. This is because filters are designed to modify the frequency response of electrical signals, which is a fundamental requirement when dealing with alternating current (AC) systems. AC contains various frequencies that can interfere with the operation of electronic devices.

Filters are used to allow certain frequencies to pass while blocking others, which is essential in applications such as audio processing, radio transmissions, and power supply systems. In contrast, direct current (DC) maintains a constant voltage and does not have frequency components to filter out.

Static current is not commonly recognized as a specific type of electrical current in the context of active electronic components, while pulsating current typically refers to a form of DC that varies over time. However, filter devices are most relevant and applicable in the context of alternating current systems. This demonstrates why the correct answer focuses on AC as the primary operating current for filter devices.