A small current flowing from base to emitter of a bipolar junction transistor (BJT) allows a larger current to flow from collector to emitter. This means that a high current load on the collector side of the BJT can easily be switched on and off completely by either giving or denying a small amount of current to base.
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NPN YouTube video
Diagram posted below the video. Using the link opens the video in a new tab!
Electronics course 8 NPN Bipolar Junction Transistor BJT switch plus capacitor fade off 2N3904
A lot of the components that I use are in this diode and transistor semiconductor kit.
Breadboard that I use. I really like it! I’ve damaged a few holes but it has lasted a lot longer, and the components insert better than the cheap boards I’ve used.
Unfortunately actual gain depends a lot on many variables. Specifics of which are best explained on the component’s datasheet and published text from reliable researchers. Circuits are simply built so that they will work reliably below a particular BJT’s minimum gain.