The cathode is the negative pole of an electrical source, where current flows into a device or circuit.
In electrical systems, the cathode serves as the electrode through which electrons enter an electrical device or circuit. In direct current (DC) systems, it is typically the negative terminal, while in alternating current (AC) systems, the cathode’s role alternates with the anode as current direction changes. This polarity-dependent behavior is fundamental in both power distribution and electronic device operation.
Cathodes are constructed from conductive materials, such as metals or specialized coatings, selected for durability and conductivity. In batteries, the cathode material directly influences energy capacity and stability. In diodes, rectifiers, and vacuum tubes, the cathode often emits electrons through heat or chemical processes, enabling the controlled flow of current. Because of its function in regulating electron movement, the cathode is a critical component in both low- and high-voltage electrical systems used in industrial, commercial, and energy applications.
Standards related to cathode use and performance are defined by organizations such as the Institute of Electrical and Electronics Engineers (IEEE) and the International Electrotechnical Commission (IEC), ensuring consistent and safe application across electrical and industrial systems.
The term “cathode” originates from the work of Michael Faraday in the 19th century, derived from Greek roots meaning “downward path.” It was first used in electrochemistry to describe the electrode where reduction occurs and electrons enter a system. Over time, the concept expanded to encompass modern electrical and electronic devices while maintaining its core definition.