Transistors

Transistors are similar to relays in the sense that when the base pin on the transistors, the circuit between collector and emitter pin is complete. Transistor have two styles, NPN and PNP. NPN allows the circuits to be complete as long as there is a positive charge supplies to the base pin. A PNP allows the circuit to be complete as long as a negative charge to be complete. Here is a picture of two NPN transistors connected. If i would have ground the charge before the signal reached the second transistor, the LED connected to it would have not been lit.