4.resistor

Component	Symbol	Picture	definition
Resistor			A resistor restricts the flow of current.
Variable Resistor (Rheostat)			This type of variable resistor with 2 contacts (a rheostat) is usually used to control current.
Variable Resistor (Potentiometer)			This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage.
Variable Resistor (Preset)			Presets are much cheaper than standard variable resistors so they are sometimes used in projects where a standard variable resistor would normally be used.