Definition

• Transistors are electrical devices vital to circuit boards and many modern electronic devices. They occur in an array of shapes, sizes and materials, but generally all transistors work to either amplify a current or allow it to pass through a particular point, turning the transistor into a type of switch. This is done by using specific materials and a tiny electrical charge to control a larger electrical current.
  
  Transistors use various semiconductive materials to create these effects, especially silicon. Silicon crystals can be synthetically grown and doped with various other elements, giving specific charges and therefore electrical properties that can be used to control the flow of the electric charge. Silicon can be given either a positive charge so that it naturally lacks electrons, or a negative charge so that it naturally gives out electrons.
  
  

Junction Transistors

• In a junction-type transistor that is used as a gateway for a much larger electrical current, there are three primary contacts made by the silicon---a base, an emitter and a collector, which together form a sandwich of different semiconductive materials. The source of the electrical charge comes from the emitter contact, and when the transistor opens the way, it will pass over to the collector and continue on its way. But the base is a type of material with an opposite charge than the surrounding two semiconductors, and as long as it is there the current cannot develop.
  
  But by applying a small electrical charge to the base (depending on what type of charge it has), the base can be changed, drawing in electrons from the emitter and creating a cycle that allows the larger charge to collect at the base and pass through to the collector. In other words, the transistor opens the gateway for the larger charge and lets it pass onward.
  
  

FETs

• FET diagram, courtesy www.madsci.org
  
  Another common type of transistor is called the FET, or field-effect transistor, which uses a source, drain and gate that take the place of emitter, collector and base of the junction transistor. This version works in a very similar fashion, allowing electrical current to flow only when a charge is sent through the gate to affect the semiconductor beneath. Although this type of transistor requires more complex materials, it requires only one type of charge to turn on.