• Diode is a semiconductor device having two electrodes. It is mainly made from Silicon or Germanium.
• Diodes have polarity. A diode has two terminals, the positive terminal is called anode and the negative terminal is called cathode. These terminals can be identified as there is a circular ring on the cathode and the terminal without ring is anode.

Diode Symbol

If positive terminal of the battery is connected to the anode and negative terminal to the cathode, diode is said to be forward biased. Diode conducts electricity and current flows from anode to cathode in this condition.

• If positive terminal of the battery is connected to the cathode and negative terminal to the anode, this is called reverse bias. Diodes do not conduct electricity in reverse bias. Current cannot flow in reverse bias.

• Thus, Current in diode can flow only in one direction i.e. from anode to cathode.
• A diode restricts the flow of current to only one direction. This property of diode is called rectification and is used to transform A.C. into D.C.
• Diode is similar to a switch which conducts electricity when it is in “ON” state.
• Major types of diode are photo diode, Light Emitting diode, Zener diode, etc.
• A diode needs only a small amount of voltage for its functioning. A silicon diode will need 0.7V to turn on. If a diode is connected across 9v battery, 0.7v will be dropped across the diode and remaining 8.3v will be available for running of the circuit.