How do Transistors Wor

A bipolar junction transistor has three terminals - Base, Collector, and Emitter corresponding to the three semi-conductor layers of the transistor. The weak input current is applied to the inner (base) layer. When there is a small change in the current or voltage at the inner semiconductor layer (base), a rapid and far larger change in current takes place throughout the whole transistor.

Pictured above is a schematic diagram of the more common NPN transistor. Below is an illustration of the same transistor using water rather than electricity to illustrate the way it functions

The illustration (from satcure-focus.com) shows pipework with three openings B (Base), C (Collector), and E (Emitter). The reservoir of water at C is the supply voltage which is prevented from getting though to E by a plunger. If water is poured into B, it pushes up the plunger letting lots of water flow from C to E. If even more water is poured into B, the plunger moves higher, and the flow of water from C to E increases.

Therefore, a small input current of electricity to the Base leads to a large flow of electricity from the Collector to the Emitter.