Electronics: An Online Guide for Beginners

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Transistors are used as switches and amplifiers. We will discuss two types of transistors: PNP and NPN transistors. Both of these transistors has 3 pins: emitter, base, collector.
There aren't any standards for where and what order the physical pins are on the transistors, so be sure to check the packaging when purchasing.

To allow electrons to flow through the collector and emitter of a PNP transistor, the following must apply:
The emitter is more positive than the base and the collector leads to the negative.

Schematic symbol

The NPN transistor is the opposite:
The collector must be more positive than the base and the emitter leads to the negative.

Schematic symbol