Tutoring science, you are naturally interested in technology.  The tutor begins an exploration of electronics.

A transistor is a device that can be used to control current flow.  Perhaps its most recognizable application is in amplifier circuits.  In that context, very small current fluctuations received by the transistor lead to very large fluctuations in its output.

A transistor’s ability to amplify current arises of its chemical composition.  It contains three “layers”:  the collector, base, and emitter.

The collector and emitter are normally rich in current carrying species, while the base is poor.  With no current to the base, it essentially “insulates” the collector from the emitter.  No current can flow across the transistor in that case.

When the base is supplied with current, it becomes conductive between the collector and the emitter.  Now, current can flow from the collector, through the base, and out the emitter.  The circuit becomes “live”.

The conductivity of the base can be described as its “gain”; this term means the amount of output current that can be expected relative to current entering the base.  The gain is typically from 50 to 200, or even more, depending on the transistor – of which there are thousands of models.  Obviously, with a gain of 150, you’ll get 150 mA out the emitter for 1 mA in the base.  This example illustrates the amplifying ability of a transistor.  Of course, they can be used in sequence to achieve any gain required.

While the explanation given above is a simplification, it is essentially correct.  I have left out some terms and complications, for now, that I will discuss in coming posts:)

Source: Wikipedia

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.