A diode is an electronic device which allows current to flow in one direction and block the current from opposite direction.
Diode is just like a one-way valve which allows current to flow in one direction. The diodes are made up of semiconductor material,germanium,silicon and selenium.
A diode is a two-terminal device.In the symbol shown below the triangular shape is showing the allowable direction of current and it is denoted as Anode.The vertical bar is representing the blocking of current in opposite direction and it is denoted by cathode.
When the diode placed in a simple lamp circuit then the diode will prevent or allow the current through the lamp, depending upon the polarity of the voltage supplied.
When the polarity of battery is such that the electrons(positive to negative) are allowed to pass through the diode and at this time the diode is called to be Forward biased.
When the polarity of battery is backward (negative to positive) then the diode blocks the current and at this time the diode is called to be Reverse biased.
