An “anode” is one of the two main terminals found in an electronic device that requires the flow of electric current. The exact definition of an anode varies depending on the specific device and context in which it’s used.
General Definition:
- The anode is the terminal where the current flows into a device from the external circuit.
Batteries:
- Primary (Non-rechargeable) Batteries: The anode is the negative terminal during discharging.
- Secondary (Rechargeable) Batteries: The anode becomes the positive terminal during charging. For instance, in a lithium-ion battery during charging, the anode is the positive terminal, but during discharging, it becomes the negative terminal.
Electrolytic Cells:
- The anode is the electrode where oxidation occurs. It can be positive or negative depending on the specific type of cell.
Diodes:
- In a diode, the anode is the positive terminal (also called the “P” side).
Electroplating:
- The anode is the electrode that is being oxidized, or corroded, as it supplies metal ions to the item being plated (cathode).
Corrosion Protection (Sacrificial Anodes):
- In systems like boats or underground pipelines, a more reactive metal (e.g., zinc) is connected as the anode, which corrodes preferentially, thereby protecting the main structure.
X-ray Tubes:
- The anode is the positive electrode, which attracts the electrons shot from the cathode, producing X-rays.
Vacuum Tubes:
- The anode, also known as the “plate” in this context, is the electrode that attracts the electrons emitted by the cathode.
In terms of symbolism:
- On a circuit diagram, anodes are usually denoted with a “plus” (+) sign if the device’s polarity matters in the context of the diagram.
The understanding of “anode” necessitates a corresponding understanding of its counterpart, the “cathode”, as these terms are relative. Depending on the device, the function and labeling of anodes and cathodes may vary.