Final answer:
The subject deals with BJTs, electronic devices that function as switches or amplifiers in circuits, utilizing a small base current to control a larger collector current.
Step-by-step explanation:
The question concerns BJT (Bipolar Junction Transistors), which are semiconductor devices used to amplify or switch electronic signals in circuits. A BJT involves an n-p-n junction and operates as a kind of electric valve controlling the flow of current. With three parts—emitter (n-type semiconductor), base (p-type semiconductor), and collector (another n-type semiconductor)—the emitter emits electrons, the base controls the flow, and the collector collects the electrons. When a positive voltage is applied to the base, a small base current (IB) allows the control of a much larger collector current (IC), thus achieving current gain in the circuit.