Zener Diode

 

A special diode, which is used to maintain a fixed voltage in a power supply.Photodiode

 

A light-sensitive diode. Which react when light is shine direct on itmay increase or decrease it resistance

TransistorsComponent Circuit Symbol Function of Component

Transistor NPN A transistor amplifies current. It can be used with other components to make anamplifier or switching circuit.Transistor PNP A transistor amplifies current. It can be used with other components to make anamplifier or switching circuit.Phototransistor  A light-sensitive transistor.

Audio and Radio DevicesComponent Circuit Symbol Function of Component

Microphone A transducer, which converts sound to electrical energy.Earphone A transducer, which converts electrical energy to sound.Loudspeaker  A transducer, which converts electrical energy to sound.Piezo Transducer  A transducer, which converts electrical energy to sound.Amplifier (general symbol)

 

An amplifier circuit with one input. Really it is a block diagram symbol becauseit represents a circuit rather than just one component.