A diode is a dispositive made of a semiconductor material, which has two terminals or electrodes
(di-ode), that act like an on-off switch. When the diode is “on”, it acts as a short circuit
and passes all current. When it is “off”, it behaves like an open circuit and passes no current.
The two terminals are different and are marked as plus and minus in figure 1. If the polarity
of the applied voltage matches that of the diode (forward bias), then the diode turns “on”.
When the applied voltage polarity is opposite (reverse bias), it turns “off”. Of course this is
the theoretical behaviour of an ideal diode, but it can be seen as a good approximation for a
real diode.
