Definition of cathode

Photonics Dictionary

cathode: A cathode is an electrode through which electric current flows out of a polarized electrical device. In different contexts, the specific role and behavior of the cathode can vary, but it generally serves as the site for reduction reactions (gain of electrons).

Reduction site: In electrochemical cells, the cathode is where reduction occurs, meaning it is the site where electrons are gained by a chemical species.

Electric current direction: The direction of electric current (conventional current flow) is considered to be from the cathode to the anode. However, the actual flow of electrons is from the anode to the cathode.

Polarity: The polarity of the cathode depends on the type of device:

Galvanic (voltaic) cells: In a galvanic cell, which generates electrical energy from a spontaneous chemical reaction, the cathode is positive because it attracts electrons from the external circuit.

Electrolytic cells: In an electrolytic cell, which uses electrical energy to drive a non-spontaneous chemical reaction, the cathode is negative because it is the source of electrons entering the cell.

Vacuum tubes and diodes: In vacuum tubes and diodes, the cathode is typically the negative electrode from which electrons are emitted.

Cathode-ray tubes: In cathode-ray tubes, the cathode emits electrons that travel through the vacuum and create an image on the screen.

Applications involving cathodes include:

Batteries: In batteries, the cathode is the positive electrode in a discharging battery (galvanic cell) and the negative electrode in a charging battery (electrolytic cell).

Electroplating: In electroplating, the object to be plated is made the cathode in an electrolytic cell.

Electronics: In electronic devices such as cathode ray tubes and vacuum tubes, the cathode is the source of electrons.