1. The Diode

2. Diodes allow electricity to flow in only one direction
Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow.
Direction of conventional current

3. switch on pd for silicon = 0.6V
non-ohmic conductor I
IMPORTANT!!!
Non-ohmic eg diode -V V
switch on pd for silicon = 0.6V
reverse bias
forward bias
Only a few materials exhibit ohmic behaviour (see the blue line on the graph) - this means “i” increases in proportion to increasing applied “V”. Some materials like wood, living tissue, plastics and even air are not ohmic. Some material combinations like pairs of semiconductors (eg Germanium/Silicon) exhibit a V - i relationship such as shown by the yellow curve. This is in effect an on-off type of material. That means they will pass current in one direction but not the other. This special property makes them extremely useful in semiconductor switches such as are found in computers and transistors that make up solid state amplifiers or mobile phones. -I

4. Rectifier diodes are used in power supplies to convert alternating current (AC) to direct current (DC), a process called rectification.

5. The diode in this circuit protects a radio or a recorder etc
The diode in this circuit protects a radio or a recorder etc... In the event that the battery or power source is connected the wrong way round, the diode does not allow current to flow. Electronic devices can be damaged or even destroyed if the polarity is reversed (positive and negative are connected to the wrong terminals).