What is symbols are commonly used on circuit diagram ?

FIXED RESISTOR

VARIABLE RESISTOR

POTENTIOMETER

THERMISTOR

LIGHT DIODE RESISTOR (LDR)

CAPACITOR (C)

VARIABLE CAPACITOR

TRIMMER CAPACITOR

POLARISED CAPACITOR

DIODE

ZENER DIODE

LED (LIGHT EMITTING DIODE)

PHOTODIODE

SCHOTTKY DIODE

RAIL

GROUND AND EARTH