William Shockley, one of the inventors of the transistor, once explained transistor-amplifiers this way:
>*”If you take a bale of hay and tie it to the tail of a mule and then strike a match and set the bale of hay on fire, and if you then compare the energy expended shortly thereafter by the mule with the energy expended by yourself in the striking of the match, you will understand the concept of amplification.”*
which seems to describe the concept but not the process.
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Shockley worked on the Junction Transistor, these days generally called a BJT or Bipolar Junction Transistor, which is also the easiest to understand amplifiers with
BJTs act like little valves, they have a collector, and emitter, and a base. The main voltage will be applied from the collector to the emitter and a small signal will be provided into the base
On a BJT, when a current flows into the base and out the emitter it opens up the valve and lets a much larger current flow from the collector to the emitter, but this isn’t an all or nothing deal there is a gain factor. If the gain factor is 20 then pushing 1 mA into the base will let 20 mA flow into the collector, 2 mA will let 40 flow, and thus your small current into the base is amplified by 20x.
MOSFETs behave similarly in their linear region, but they’re controlled by a voltage on the gate not a current.
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