colors,
We are talking about a NPN transistor in the active region. The positive voltage of the base attracts the charge carriers (electrons) from the emitter. Some small percentage of the electrons get sidetracked and constitute the base current, but most are attracted by the higher positive collector voltage and pass through the relatively thin base region into the collector circuit and the load. So the emitter supplies the electrons, the base voltage controls the electron flow, and the collector receives the electrons because they are attracted to the relatively higher positive collector voltage.
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